(Commentaire sous forme de note FLEX User Group
11/11/1997 18:04:36
This document has been created
on behalf of the FLEX User Group
to keep FLEX Alive.
Many thanks to the copyright holder
of this manual for releasing the
copyright to the Flex User Group.)
FLEX Assembler 


Technical Systems Consultants, Inc. 



COPYRIGHT (c) 1979 by 
Technical Systems Consultants, 
Inc. 
P.O. Box 2570 
West Lafayette, Indiana 47906 
All Rights Reserved 



Table of Contents

Table of Contents

 I. Introduction 1

 II. Getting the System Started 2

 III. Assembler Operation 7

 IV. The Instruction Set 13

 V. Standard Directives 25

 VI. Conditional Assembly 33

 VII. Macros 37 

VIII. Special Features 46

 IX. Object Code Production 52

 X. Error and Warning Messages 53

 XI. Adapting to Your System 55 


TSC 6809 Assembler 


TSC 6809 Assembler 

TSC 6809 Assembler 
The 6809 Mnemonic Assembler is a fast and powerful disk based assembler 
interfaced to the FLEXt disk operating system. It accepts all standard 
Motorola mnemonics for the 6809 instruction set as well as all standard 
6800 and 6801 mnemonics. Macros and conditional assembly are supported 
as well as numerous other directives for convenient assembler control. 
The assembler executes in two passes and can accept any size file on the 
disk so long as sufficient memory is installed to contain the symbol 
table. Output is in the form of a binary disk file or a hexadecimal tape 
as well as an assembled listing output which may be routed to a printer 
or to a disk file through the facilities of FLEX. 

This manual is by no means intended to teach the reader assembly 
language programming nor even the full details of the 6809 instruction 
set. It assumes the user has a working knowledge of assembly language 
programming and a manual describing the 6809 instruction set and 
addressing modes in full. The former can be acquired through any of a 
large number of books available on assembly programming, the latter from 
the 6809 hardware manufacturer or seller. 

Throughout the manual a couple of notational conventions are used which 
are explained here. The first is the use of angle brackets (’<’ and 
’>’). These are often used to enclose the description of a particular 
item. This item might be anything from a filename to a macro parameter. 
It is enclosed in angle brackets to show that it is a single item even 
though the description may require several words. The second notation 
is the use of square brackets (’[’ and ’]’). These are used to enclose 
an optional item. 

FLEX is a trademark of Technical Systems Consultants, Inc. 

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TSC 6809 Assembler 

TSC 6809 Assembler 
GETTING THE SYSTEM STARTED 
The disk version of the 6809 Mnemonic Asssembler is very simple to use. 
There are no built-in editing functions - you must have a previously 
edited source file on disk before using the assembler. This file must 
be a standard FLEX text file which is simply textual lines terminated by 
a carriage return. There should be no line numbers or control 
characters (except for the carriage returns) in the file. When you have 
both the assembler and the edited source file on a disk or disks which 
are inserted in a powered up system, you are ready to begin. 

The Command Line 

The very minimum command line necessary to execute an assembly is as 
follows:

 +++ASMB,<filename> 

The three plus signs are FLEX’s ready prompt, ASMB is the name of the 
assembler file (it has a .CMD extension), and the <filename> is the 
standard FLEX specification for the source file you wish to assemble. 
The <filename> defaults to a .TXT extension and to the assigned working 
drive if an explicit extension and drive number are not given. In this 
and forthcoming example command lines, a comma is used to separate 
items. It is also possible to use a space or spaces in this capacity. 

As stated, this is the very minimum command which can be used. It is 
possible to supply many more parameters or options to the assembler, but 
if left off as in this example, the assembler will assume default 
parameters. Perhaps the most important options available are the two 
associated with output. We say two because there are two types of 
output available from the assembler: object code output and assembled 
source listing output. The options regarding the assembled source 
listing output will be described a little later. 

The object code can be in the form of a binary disk file, a hex output 
to tape, or no object code output at all. Since no specifications are 
made concerning object code output in the above example, the assembler 
will assume the default case which is a binary disk file. Since no name 
was specified, the output binary file will assume the same name as the 
input source file specified but with a .BIN extension. If such a file 
already exists, you will be asked:

 DELETE OLD BINARY (Y-N)? 

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TSC 6809 Assembler 

TSC 6809 Assembler 

If you wish to create a binary file by another name or extension, you 
may do so by placing the desired file specification on the command line 
as follows:

 +++ASMB,<input file spec>,<binary file spec> 

This binary file specification will default to a .BIN extension and to 
the assigned working drive. If a file by that name already exists on 
the specified drive, you will be prompted as described above. 

Specifying Assembly Options 

Now we shall go one step further and add a set of single character 
option flags which may be set on the command line as follows:

 +++ASMB,<input file spec>[,<binary file spec>][,+<option list>] 

The square brackets indicate that the binary file spec and the option 
list are optional. The plus sign is required to separate the option 
list from the file specifications. The <option list> is a set of single 
character flags which either enable or disable a particular option. In 
all cases they reverse the sense of the particular option from its 
default sense. There may be any number of options specified and they 
may be specified in any order. There may not be spaces within the 
option list. Following is a list of the available options and what they 
represent: 

B 
Do not create a binary file on the disk. No binary file will be 
created even if a binary file name is specified. This is useful 
when assembling a program to check for errors before the final 
program is completed or when obtaining a printed source listing. 

L 
Suppress the assembled listing output. If not specified, the 
assembler will output each line as it is assembled in pass 2, 
Those lines containing errors will always be printed regardless of 
whether or not this option is specified. 

S 
Suppress the symbol table output. The assembler normally prints 
out a sorted symbol table at the end of an assembly. This option 
suppresses that output. Note that the L option will not suppress 
the symbol table output, just the source itself. 

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TSC 6809 Assembler 

G 
Turns off printing of multiple line object code instructions. 
Certain directives (FCB, FDB, and FCC) can produce several lines 
of output listing for only one instruction line. This option 
prints the first line of output from such an instruction (the line 
which contains the source) but suppresses the printing of the 
subsequent lines which contain only object code information. 

N 
Enables the printing of decimal line numbers on each output line. 
These numbers are the consecutive number of the line as read by 
the assembler. Error lines are always output with the line number 
regardless of the start of this option. 

T 
Produce a hex output directly to tape. This output is formatted 
in the standard Motorola ’S1-S9’ format. Consult the section on 
object code production for further details. 

Y 
This option overrides the prompt for deleting an existing binary 
file. In other words, if the Y option (stands for YES) is 
specified, an existing binary file of the same name as the one to 
be created will be automatically deleted without a prompt. 

D 
Suppress printing of the date in the header at the top of each 
output page. The assembler normally picks up the current date 
from FLEX and prints it in the header. This option causes the 
date to be omitted. 

W 
Suppress warning messages. The 6809 assembler is capable of 
reporting a number of warning messages as well as an indicator of 
long jumps and branches that could be shortened. This option 
suppresses the printing of these messages and indicators. 

P<no> This option allows the programmer to specify a page number at 
which to start printing of the assembled listing. Complete 
instructions can be found in the next paragraph. 

Specifying a Starting Page Number 

As mentioned in the ’P’ option above, it is possible to specify a 
particular page number at which printing of the assembled listing should 
commence. All output before that page is suppressed INCLUDING ERROR 
LINES! When the specified page is hit, printing begins and continues to 
the end of the assembly. Note that it is possible to suspend or to 
completely terminate an assembly during output by use of the escape or 
escape/return sequence found in FLEX. The desired page number is 
specified right with the ’P’ option in the option list. It must 
directly follow the ’P’ and should be a decimal number from 1 to 65,536. 
The page number itself must be directly followed by a non-alphanumeric 
character (terminator) such as a comma or space. This implies that the 
’P’ option, if specified, MUST BE THE LAST OPTION SPECIFIED. The page 
number may also be followed or terminated by a plus sign as used in the 
following paragraph. It is also important to note that the PAG mode 
must be selected (pagination turned on) in order for the ’P’ option to 
have any effect. The PAG mode may be turned on as described in the 
section on Standard Directives. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

The assembler has a facility for passing information from the command 
line directly into the source program. A maximum of three pieces of 
information or "command line parameters" may be passed to the program. 
These parameter are simply strings of characters that will be 
substituted into the source listing as it is read in by the assembler. 
These parameters are expressed in the command line in the manner shown 
here:

 +++ASMB,<in file>,<binary file>,+<options>,+<prm.l>,<prm.2>,<prm.3> 

The parameters are optional but must be separated from the rest of the 
line by the second plus sign and from each other by commas. As stated, 
these parameters are simply strings of characters. They may be supplied 
in two ways: as a string of characters enclosed by a delimiter or just a 
string of characters with no spaces or commas embedded. The 
"delimiters" which can be used to enclose a string are the single quote 
(’) and the double quote ("). Either can be used but for a particular 
string the beginning delimiter and the ending delimiter must be the 
same. The reason for using a delimited string is to pass in a string 
with commas and/or spaces which cannot be in an un-delimited string. 
Note that if one wishes to enter a command line parameter but no 
options, he must still place both plus signs in the command as seen in 
this example command line:

 +++ASMB,ANYFILE,++PARAMETER1,PARAMETER2 

For further information on command line parameters and how to specify 
where in the source program these parameters should be substituted, see 
the section on Special Features. 

OUTPUTTING TO A HARDCOPY DEVICE 

The assembler does not have a built in means for outputting the 
assembled listing to a hardcopy device. This operation is, however, 
available through the facilities of FLEX. To do so one must use the ’P’ 
command provided with FLEX. This ’P’ command reads a printer driver 
file which you can supply to output to any hardcopy device you want. It 

effectively switches the output of the assembler from going to the 
terminal to going to the printer. For example: 
+++P,ASMB,TESTFILE 

would cause the assembled listing of the source file TESTFILE.TXT to be 
output to the printer. For further details of use of the ’P’ command 
the FLEX User’s Manual and Advanced Programmer’s Guide. 

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TSC 6809 Assembler 

TSC 6809 Assembler 
: 

ASMB,TEST 
Assembles a file called TEST-TXT on the assigned working drive 
and creates a binary file called TEST.BIN on the same drive. 
The assembled listing is output to the terminal as is the 
symbol table. 

ASMB,TEST,+LS 
Same as before except that no listing is output (except for 
any lines with errors) and no symbol table is output. 

ASMB,0.TEST,1.TEST.CMD,+LSY 
Assembles a file from drive 0 called TEST.TXT and produces a 
binary file on drive 1 called TEST.CMD. No listing or symbol 
table is output and if a file by the name of TEST.CMD already 
resides on drive 1, it will be automatically deleted before 
the assembly starts. 

l.ASMB,0.TEST.BAK,+BNGS 
Loads the assembler itself from drive 1 and assembles a file 
called TEST.BAK found on drive 0. No binary file is produced. 
The assembled listing is output with line numbers turned on 
and multiple line generated code turned off. No symbol table 
is printed. 

ASMB,0.TEST.BAK,+GSBNP26 
This command performs just like the last with two exceptions. 
First, the assembler itself is loaded from the whatever the 
assigned system drive is. Second, the assembled listing 
output does not begin until the assembler reaches page number

 26. 
0.ASMB,0.ASMB,0.ASMB,+GW,+MINI,’ASSEMBLER FOR 5" DISK’ 
This command looks a little confusing, but it was done to 
accentuate the method in which default extensions work. The 
assembler itself (a file called ASMB.CMD) is loaded from drive 
0, the file called ASMB.TXT found on drive 0 is assembled, and 
a binary file is produced on drive 0 by the name ASMB.BIN. 
Note that it was not necessary to specify the binary file name 
in this case since ASMB.BIN is what the default would have 
been. The assembled listing is output with multiple line code 
generation suppressed and warning messages suppressed. There 
are two parameters which may be passed into the source 
listing. The first is the single word ’MINI’. The second 
parameter is the entire string, ’ASSEMBLER FOR 5" DISK’, 
excluding the single quote delimiters (everything starting 
with the A and ending with the K). 

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TSC 6809 Assembler 

TSC 6809 Assembler 
ASSEMBLER OPERATION & SOURCE LINE COMPONENTS 
The TSC Assembler is a 2 pass assembler. During pass one a symbolic 
reference table is constructed and in pass two the code is actually 
assembled, printing a listing and outputting object code if desired. 
The source may be supplied in free format as described below. Each line 
of source consists of the actual source statement terminated with a 
carriage return (0D hex). The source must be comprised of ASCII 
characters with their parity or 8th bit cleared to zero. Special 
meaning is attached to many of these characters as will be described 
later. Control characters (00 to FF hex) other than the carriage return 
(0DH) are prohibited from being in the actual source statement part of 
the line. Their inclusion in the source statement will produce 
undefined results. Each source line is comprised of up to four fields: 
Label, Opcode, Operand, and Comment. With two exceptions, every line 
must have an opcode while the other fields may or may not be optional. 
These two exceptions are:

 1) "Comment Lines" may be inserted anywhere in the source and are 
ignored by the assembler during object code production. 
Comment lines may be either of two types:

 a) Any line beginning with an asterisk (hex 2A) in column 
one.

 b) A null line or a line containing only a carriage return. 
While this line can contain no text, it is still 
considered a comment line as it causes a space in the 
output listing.

 2) lines which contain a label but no opcode or operand field. 

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TSC 6809 Assembler 

TSC 6809 Assembler 
S 


The four fields are described here along with their format 
specifications. The fields are free format which means there may be any 
number of spaces separating each field. In general, no spaces are 
allowed within a field. 

LABEL OR SYMBOL FIELD: 

This field may contain a symbolic label or name which is assigned the 
instruction’s address and may be called upon throughout the source 
program.

 1) The label must begin in column one and must be unique. Labels 
are optional. If the label is to be omitted, the first 
character of the line must be a space.

 2) A label may consist of letters (A-Z or a-z), numbers (0-9), or 
an underscore (_ or 5F hex). Note that upper and lower case 
letters are not considered equivalent. Thus ’ABC’ is a 
different label from ’Abc’.

 3) Every label must begin with a letter. 
4) Labels may be of any length, but only the first 6 characters 
are significant. 
5) The label field must be terminated by a space or a return. 

OPCODE FIELD: 

This field contains the 6809 opcode (mnemonic) or pseudo-op. It 
specifies the operation that is to be performed. The pseudo-ops 
recognized by this assembler are described later in this manual.

 1) The opcode is made up of letters (A-Z or a-z) and numbers 
(0-9). In this field, upper and lower case may be used 
interchangeably.

 2) This field must be terminated by a space if there is an 
operand or by a space or return if there is no operand. 

OPERAND FIELD: 

The operand provides any data or address information which may be 
required by the opcode. This field may or may not be required, 
depending on the opcode. Operands are generally combinations of 
register specifications and mathematical expressions which can include 
constants, symbols, ASCII literals, etc. as explained later. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

 2) This field is terminated with a space or return.

 3) Any of several types of data may make up the operand: register

 specifications, numeric constants, symbols, ASCII literals,

 and the special PC designator. 

COMMENT FIELD: 

The comment field may be used to insert comments on each line of source. 
Comments are for the programmer’s convenience only and are ignored by 
the assembler.

 1) The comment field is always optional.

 2) This field must be preceded by a space.

 3) Comments may contain any characters from SPACE (hex 20) thru

 DELETE (hex 7F).

 4) This field is terminated by a carriage return.

 REGISTER SPECIFICATION 

Many opcodes require that the operand following them specify one or more 
registers. EXG and TFR require two registers specified, push and pull 
allow any number, and the indexed addressing mode requires specification 
of the register by which indexing is to be done. The following are 
possible register names:

 A,B,CC,DP,X,Y,U,S,D,PC 

The EXG and TFR instructions require two register specs separated by a 
comma. The push and pull instructions allow any number of registers to 
be specified, again, separated by commas. Indexed addressing requires 
one of X,Y,U, or S as explained under the indexed addressing mode 
description.

 EXPRESSIONS 

Many opcodes require that the operand supply further data or information 
in the form of an expression. This expression may be one or more items 
combined by any of four operator types: arithmetic, logical, relational, 
and shift. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

ITEM TYPES: 

The "item or items" used in an expression may be any of four types as 
listed below. These may stand alone or may be intermixed by the use of 
the operators.

 1) NUMERICAL CONSTANTS: Numbers may be supplied to the assembler 
in any of the four number bases shown below. The number given 
will be converted to 16 bits truncating any numbers greater 
than that. If 8 bit numbers are required, the 16 bit number 
will then be further truncated to 8 bits with notification of 
such if warning messages are enabled. To specify which number 
base is desired, the programmer must supply a prefix character 
to a number as detailed below.

 BASE PREFIX CHARACTERS ALLOWED

 Decimal none 0 thru 9 
Binary % 0 or 1 
Octal @ 0 thru 7 
Hexadecimal $ 0 thru 9, A thru F

 If no prefix is assigned, the assembler assumes the number to 
be decimal.

 2) ASCII CONSTANTS: The binary equivalent of a single ASCII 
printable character may be supplied to the assembler by 
preceding it with a single quote. The character should be 
between 20 and 7F hex.

 3) LABELS: Labels which have been assigned some address or 
constant value may be used in expressions. As described above 
under the label field, a label is comprised of letters, 
digits, and hyphens beginning with a letter. The label may be 
of any length, but only the first 6 characters are 
significant. Any label used in the operand field must be 
defined elsewhere in the program.

 4) PC DESIGNATOR: The asterisk (*) has been set aside as a 
special PC designator (Program Counter). It may be used in an 
expression just as any other value and is equal to the address 
of the current instruction. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

As mentioned previously, the four classes of operators are: arithmetic, 
logical, relational, and shift. These operators permit assembly-time 
operations such as addition or division to take place. "Assembly-time" 
means that the expression is evaluated during the assembly and the 
result becomes a permanent part of your program.

 a) ARITHMETIC OPERATORS 
The arithmetic operators are as follows:


 Operator Meaning

 + Unary or binary addition 
-Unary or binary subtraction 
* Multiplication 
/ Division (any remainder is discarded) 
b) LOGICAL OPERATORS 
The logical operators are as follows:


 Operator Meaning

 & logical AND operator 
| Logical OR operator 
! Logical NOT operator 
>> Shift right operator 
<< Shift left operator

 The logical operations are full 16 bit operations. 
In other words for the AND operation, every bit from 
the first operand or item is individually AND’ed with 
its corresponding bit from the second operand or item. 
The shift operators shift the left term the number of 
places indicated by the right term. Zeroes are 
shifted in and bits shifted out are lost.

 c) RELATIONAL OPERATORS 
The relational operators are as follows:


 Operator Meaning

 = Equal 
< Less than 
> Greater than 
<> Not equal 
<= Less than or equal 
>= Greater than or equal

 The relational operations yield a true-false result. 
If the evaluation of the relation is true, the resulting 
value be all ones. If false, the resulting value will 
will be all zeros. Relational operations are generally 
used in conjunction with conditional assembly as shown 
in that section. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

Certain operators take precedence over others in an expression. This 
precedence can be overcome by use of parentheses. If there is more than 
one operator of the same priority level and no parentheses to indicate 

the order in which they should be evaluated, 
carried out in a left to right order. 
then the operations are 
The following list classifies 
(highest priority first):
the operators in order of precedence 
1) Parenthesized expressions 
2) Unary + and 3) 
Shift operators 
4) Multiply and Divide

 5) Binary Addition and Subtraction 
6) Relational Operators 
7) Logical NOT Operator 
8) Logical AND and OR Operators 

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TSC 6809 Assembler 

TSC 6809 Assembler 
The INSTRUCTION SET 
This section is a quick introduction to the 6809 architecture and 
insruction set. It is by no means complete. The intention is to 
familiarize the user who is already proficient at 6800 assembly language 
programming with the basic structure of 6809 assembly language. For 
more complete details on the 6809 instruction set you should obtain the 
proper documentation from the hardware manufacturer. 

PROGRAMMING MODEL 

The 6809 microprocessor has 9 registers that are accessible by the 
programmer. Four of these are 8-bit registers while the other five are 
16-bit registers. Two of the 8-bit registers can, in some instances, be 
referenced as one 16-bit registers. The registers are as follows:

 The ’A’ accumulator (A) 8 bit 
The ’B’ accumulator (B) 8 bit 
The Condition Code register (CC) 8 bit 
The Direct Page register (DP) 8 bit 
The ’X’ index register (X) 16 bit 
The ’Y’ index register (Y) 16 bit 
The User stack pointer (U) 16 bit 
The System stack pointer (5) 16 bit 
The Program Counter (PC) 16 bit 


The A and B accumulators can often be referenced as one 16-bit register 
represented by a ’D’ (for Double-accumulator). In these cases, the A 
accumulator is the most significant half. 

THE 
ADDRESSING MODES 

There are several possible addressing modes in the 6809 instruction set. 
One of the best features of the 6809 is the consistency or regularity 
built into the instruction set. For the most part, any instruction 
which addresses memory can use any of the addressing modes available. 
It is not necessary to remember which instructions can use which 
addressing modes, etc. The addressing modes and a brief description of 
each follow. 

1) 
Inherent 
Inherent addressing refers to those instructions which have no 
addressing associated with them. 
Example: ABX add B accumulator to X 

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TSC 6809 Assembler 

TSC 6809 Assembler 
) 
Accumulator 
Accumulator addressing is done in those instructions which can 
specify the A or B accumulator. In some cases this may be the 
16-bit D accumulator. 
Example: DECA decrement the A accumulator 

3) 
Immediate 
In Immediate addressing the byte or bytes following the opcode are 
the information being addressed. These byte or bytes are specified 
as part of the instruction. 
Example: LDA #8 load immediate value (8) into A 

4) 
Relative - Long and Short 
In Relative addressing, the value of the byte(s) immediately 
following the opcode (1 if short, 2 if long) are added as a two’s 
complement number to the current value of the program counter (PC 
register) to produce a new PC location. In the source code, the 
programmer specifies the desired address to which execution should 
be transferred and the assembler determines the correct offset to 
place after the opcode. 
Example: LBRA THERE the program will branch to THERE 

5) 
Extended 
In Extended addressing, the two bytes (16-bits) following the opcode 
are used as an absolute memory address value. 
Example: LDA $1000 load A from memory location 1000 hex 

6) 
Direct 
In Direct addressing, the single byte (8-bits) following the opcode 
is used as a pointer into a 256-byte window or "page" of memory. 
The page used for this purpose is the one currently found in the 
Direct Page register. Thus, the effective address is a 
concatenation of the Direct Page register as the most significant 
half and the byte following the opcode as the least significant 
half. 
Example: LDA $22 load A from memory location $XX22 where XX

 represents the contents of the DP register 

7) 
Extended Indirect 
In Extended Indirect addressing, the 16-bit value following the 
opcode is used to point to two bytes in memory which are used as the 
effective address. 
Example: LDA [$A012] loads A from the address stored at

 locations $A012 and $A013 

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TSC 6809 Assembler 

TSC 6809 Assembler 
) 
Indexed 
The Indexed addressing mode of the 6809 is an extremely powerful 
method of specifying addresses which is, in general, some sort of 
offset from the value stored in one of the registers X, Y, U, S, or 
PC. There are several forms of indexed addressing which could each 
be considered an addressing mode in itself. We will, however, 
discuss each as a subset of Indexed addressing in general. Note 
that except for the Auto-increment and Auto-decrement modes, 
determining the effective address has no effect on the register 
being used as the index. 

8a) Constant-Offset Indexed 
This mode uses a two’s complement offset value found in the byte or 
bytes following the opcode. The offset is added to the contents of 
the specified register to produce a 16-bit effective address. The 
offset may be represented as a number, a symbol, or any valid 
expression. It can be either positive or negative and can be a full 
16-bits. 
Example: LDA 0,X loads A from location pointed to by X

 LDA 5216,Y loads A from (Y) plus 5216 
LDA -36,U loads A from (U) minus 36 
LDA VAL,S loads A from (S) plus VAL 

8b) Accumulator Indexed 
In Accumulator indexing, the contents of the specified accumulator 
(A, B, or D) are added to the specified indexing register as a two’s 
complement value. The result is the effective address. 
Example: LDA B,Y loads A from (B)+(Y)

 LDX D,S loads X from (D)+(S) 

8c) Auto-Increment 
The contents of the selected register are used as the effective 
address with no offset permitted. After that effective address has 
been determined, the selected register is incremented by one (for 
single plus sign) or two (double plus sign). 
Example: LDA 0,X+ loads A from X then bumps X by 1

 LDD ,Y++ loads D from Y then bumps Y by 2 

8d) Auto-Decrement 
In auto-decrementing, the selected register is first decremented by 
one (single minus sign) or two (double minus sign). The resulting 
value, with no offset, is used as the effective address. 
Example: LDA 0,-U decrements U by 1 then loads A from address in U

 LDU ,--S decrements S by 2 then loads U from address in S 

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TSC 6809 Assembler 

TSC 6809 Assembler 

Indexed Indirect Addressing 

All the Indexed Addressing modes above can also be used in an indirect 
fashion by enclosing the operand in square brackets. When this is done, 
the effective address as described in all the above modes is no longer 
the final effective address. Instead, the two bytes pointed to by that 
address are used as the effective address.

 Examples: LDA [,X] loads A from the address pointed to by X 
LDX [D,U] loads X from the address pointed 
to by (U)+(D) 

If auto-increment or auto-decrement addressing is done in an indirect 
fashion, they must be a double increment (two plus signs) or double 
decrement (two minus signs). 

PC Relative Addressing 

Indexing may be done from the PC register just as from the X, Y, U, or 

S. The general use of indexing from the PC register is to address some 
value in a position-independent manner. Thus if we address some value 
at the current PC plus 10, no matter where the program executes the 
value will always be addressed. The programmer does not usually know 
what that constant offset should be, he knows the address of the value 
he wants to access as an absolute value for the program as assembled. 
Thus a mechanism has been included in the assembler to automatically 
determine the offset from the current PC to that absolute address. This 
mechanism is called PC Relative Addressing. The value specified in a PC 
Relative address operand is the absolute value. The assembler takes the 
difference between this absolute value and the current PC and generates 
that offset as part of the assembled code for the instruction. PC 
Relative Addressing is distinguished from normal PC Offset Indexing by 
the use of ’PCR’ as the register name instead of ’PC’. 
Example: LEAX STRING,PCR 
this instruction determines the offset 
between the PC and STRING and uses it 
as an offset for the PC register to 
determine the effective address 


- 16 



TSC 6809 Assembler 

TSC 6809 Assembler 

The 6809 assembler has a mechanism for forcing the assembler to perform 
either direct or extended addressing. Under normal conditions, the 
assembler will use direct addressing when possible. To force the 
assembler to use extended addressing no matter what the conditions, 
simply precede the operand with a greater than sign (’>’). For example, 
suppose the DP register was set to $00 (this is the default on reset of 
the cpu), and that we have a label, BUFPNT, which is at memory location 
$0010. Normally the instruction:

 LDX BUFPNT 

would be assembled with direct addressing. If we wished to force 
extended addressing we could simply enter:

 LDX >BUFPNT 

and the assembler would use extended addressing. 

The same capability exists for forcing direct addressing by preceding 
the operand with a less than sign (’<’). For example:

 LDX <BUFPNT 

would force direct addressing. Note that in both cases the greater than 
or less than sign must be the first character in the operand. 

- 17 



TSC 6809 Assembler 

TSC 6809 Assembler 

This section contains a brief listing of all the mnemonics accepted by 
the 6809 assembler. They are listed in four sections, standard 6809 
with alternate 6800, 6800 mnemonics not found in 6809, 6801 mnemonics, 
and non-standard convenience mnemonics. Before the listing, we must 
setup some notational conventions:

 (P) 
Operand containing immediate, extended, direct, or 
indexed addressing. 
(Q) 
Operand containing extended, direct, or indexed 
addressing. 
(T) Operand containing indexed addressing only. 
R Any register specification: A, B, X, Y, U, S, PC, 
CC, DP, or D.

 dd 8 bit data value

 dddd 16 bit data value 

6809 MNEMONICS WITH 6800 ALTERNATES 

ABX 
Add B into X 
SOURCE FORM: ABX 

ADC 
Add with carry into register 
SOURCE FORM: ADCA (P); ADCB (P) 
6800 ALTERNATES: ADC A (P); ADC B (P) 

ADD 
Add into register 
SOURCE FORM: ADDA (P); ADDB (P); ADDD (P) 
6800 ALTERNATES: ADD A (P); ADD B (P) 

AND 
Logical ’AND’ into register 
SOURCE FORM: ANDA (P); ANDB (P) 
6800 ALTERNATES: AND A (P); AND B (P) 

ANDCC 
Logical ’AND’ immediate into CC 
SOURCE FORM: ANDCC #dd 

ASL 
Arithmetic shift left 
SOURCE FORM: ASLA; ASLB; ASL (Q) 
6800 ALTERNATES: ASL A; ASL B 

- 18 



TSC 6809 Assembler 

TSC 6809 Assembler 
Arithmetic shift right 
SOURCE FORM: ASRA; ASRB; ASR (Q) 
6800 ALTERNATES: ASR A; ASR B 
BCC, LBCC Branch (short or long) if carry clear 
SOURCE FORM: BCC dd; LBCC dddd 
BCS, LBCS Branch (short or long) if carry set 
SOURCE FORM: BCS dd; LBCS dddd 
BEQ, LBEQ Branch (short or long) if equal 
SOURCE FORM: BEQ dd; LBEQ dddd 
BGE, LBGE Branch (short or long) if greater than or equal 
SOURCE FORM: BGE dd; LBGE dddd 
BGT, LBGT Branch (short or long) if greater than 
SOURCE FORM: BGT dd; LBGT dddd 
BHI, LBHI Branch (short or long) if higher 
SOURCE FORM: BHI dd; LBHI dddd 
BHS, LBHS Branch (short or long) if higher or same 
SOURCE FORM: BHS dd; LBHS dddd 
BIT Bit test 
SOURCE FORM: BITA (P); BITB (P) 
6800 ALTERNATES: BIT A (P); BIT B (P) 
BLE, LBLE Branch (short or long) if less than or equal to 
SOURCE FORM: BLE dd; LBLE dddd 
BLO, LBLO Branch (short or long) if lower 
SOURCE FORM: BLO dd; LBLO dddd 
BLS, LBLS Branch (short or long) if lower or same 
SOURCE FORM: BLS dd; LBLS dddd 
BLT, LBLT Branch (short or long) if less than 
SOURCE FORM: BLT dd; LBLT dddd 
BMI, LBMI Branch (short or long) if minus 
SOURCE FORM: BMI dd; LBMI dddd 
BNE, LBNE Branch (short or long) if not equal 
SOURCE FORM: BNE dd; LBNE dddd 
BPL, LBPL Branch (short or long) if plus 
SOURCE FORM: BPL dd; LBPL dddd 

- 19 



TSC 6809 Assembler 

TSC 6809 Assembler 
Branch (short or long) always 
SOURCE FORM: BRA dd; LBRA dddd 
BRN, LBRN Branch (short or long) never 
SOURCE FORM: BRN dd; LBRN dddd 
BSR, LBSR Branch (short or long) to subroutine 
SOURCE FORM: BSR dd; LBSR dddd 
BVC, LBVC Branch (short or long) if overflow clear 
SOURCE FORM: BVC dd; LBVC dddd 
BVS, LBVS Branch (short or long) if overflow set 
SOURCE FORM: BVS dd; LBVS dddd 
CLR Clear 
SOURCE FORM: CLRA; CLRB; CLR (Q) 
6800 ALTERNATES: CLR A; CLR B 
CMP Compare 
SOURCE FORM: CMPA (P); CMPB (P); CMPD (P); CMPX (P); 
CMPY (P); CMPU (P); CMPS (P) 
6800 ALTERNATES: CMP A (P); CMP B (P); CPX (P) 
COM Complement (One’s complement) 
SOURCE FORM: COMA; COMB; COM (Q) 
6800 ALTERNATES: COM A; COM B 
CWAI Clear and wait for interrupt 
SOURCE FORM: CWAI #dd 
DAA Decimal adjust accumulator A 
SOURCE FORM: DAA 
DEC Decrement 
SOURCE FORM: DECA, DECB, DEC (Q) 
6800 ALTERNATES: DEC A; DEC B 
EOR Exclusive ’OR’ 
SOURCE FORM: EORA (P); EORB (P) 
6800 ALTERNATES: EOR A (P); EOR B (P) 
EXG Exchange registers 
SOURCE FORM: EXG Rl,R2 
INC Increment 
SOURCE FORM: INCA, INCB, INC (Q) 
6800 ALTERNATES: INC A; INC B 

- 20 



TSC 6809 Assembler 

TSC 6809 Assembler 
P 
Jump to address 
SOURCE FORM: JMP dddd 

JSR 
Jump to subroutine at address 
SOURCE FORM: JSR dddd 

LD Load register from memory 
SOURCE FORM: LDA (P); LDB (P); LDD (P); LDX (P); 
LDY (P); LDU (P); LDS (P) 
6800 ALTERNATES: LDAA (P); LDAB (P); LDA A (P); LDA B (P) 

LEA 
Load effective address 
SOURCE FORM: LEAX (T); LEAY (T); LEAU (T); LEAS (T) 

LSL 
Logical shift left 
SOURCE FORM: LSLA; LSLB; LSL (Q) 

LSR 
Logical shift right 
SOURCE FORM: LSRA; LSRB; LSR (Q) 
6800 ALTERNATES: LSR A; LSR B 

MUL 
Multiply accumulators 
SOURCE FORM: MUL 

NEG 
Negate (Two’s complement) 
SOURCE FORM: NEGA; NEGB; NEG (Q) 
6800 ALTERNATES: NEG A; NEG B 

NOP 
No operation 
SOURCE FORM: NOP 

OR 
Inclusive ’OR’ into register 
SOURCE FORM: ORA (P); ORB (P) 
6800 ALTERNATES: ORAA (P); ORAB (P); ORA A (P); ORA B (P) 

ORCC 
Inclusive ’OR’ immediate into CC 
SOURCE FORM: ORCC #dd 

PSHS 
Push registers onto system stack 
SOURCE FORM: PSHS (register list); PSHS #dd 
6800 ALTERNATES: PSRA; PSHB; PSH A; PSH B 

PSHU 
Push registers onto user stack 
SOURCE FORM: PSHU (register list); PSHU #dd 

PULS 
Pull registers from system stack 
SOURCE FORM: PULS (register list); PULS #dd 
6800 ALTERNATES: PULA; PULB; PUL A; PUL B 

PULU 
Pull registers from user stack 
SOURCE FORM: PULU (register list); PULU #dd 

- 21 



TSC 6809 Assembler 

TSC 6809 Assembler 
L 
Rotate left

 SOURCE FORM: ROLA; ROLB; ROL (Q)

 6800 ALTERNATES: ROL A; ROL B 

ROR 
Rotate right

 SOURCE FORM: RORA; RORB; ROR (Q)

 6800 ALTERNATES: ROR A; ROR B 

RTI 
Return from interrupt 
SOURCE FORM: RTI 

RTS 
Return from subroutine 
SOURCE FORM: RTS 

SBC 
Subtract with borrow

 SOURCE FORM: SBCA (P); SBCB (P);

 6800 ALTERNATES: SBC A (P); SBC B (P) 

SEX 
Sign extend 
SOURCE FORM: SEX 

ST Store register into memory 
SOURCE FORM: STA (P); STB (P); STD (P); STX (P); 
STY (P); STU (P); STS (P) 
6800 ALTERNATES: STAA (P); STAB (P); STA A (P); STA B (P) 

SUB 
Subtract from register

 SOURCE FORM: SUBA (P); SUBB (P); SUBD (P)

 6800 ALTERNATES: SUB A (P); SUB B, (P) 

SWI 
Software interrupt 
SOURCE FORM: SWI 

SWI2 
Software interrupt 2 
SOURCE FORM: SWI2 

SWI3 
Software interrupt 3 
SOURCE FORM: SWI3 

SYNC 
Synchronize to interrupt 
SOURCE FORM: SYNC 

TFR 
Transfer register to register 
SOURCE FORM: TFR Rl,R2 

TST Test

 SOURCE FORM: TSTA; TSTB; TST (Q)

 6800 ALTERNATES: TST A; TST B 

- 22 



TSC 6809 Assembler 

TSC 6809 Assembler 
S 


ABA Add B to A 
CBA Compare B to A 
CLC Clear carry bit 
CLI Clear interrupt mask 
CLV Clear overflow bit 
DES Decrement stack pointer 
DEX Decrement X 
INS Increment stack pointer 
INX Increment X 
SBA Subtract B from A 
SEC Set carry bit 
SEI Set interrupt mask 
SEV Set overflow bit 
TAB Transfer A to B 
TAP Transfer A to CC 
TBA Transfer B to A 
TPA Transfer CC to A 
TSX Transfer S to X 
TXS Transfer X to S 
WAI Wait for interrupt 

- 23 



TSC 6809 Assembler 

TSC 6809 Assembler 
S 


ASLD Arithmetic shift left D 
LSRD Logical shift right D 
PSHX Push the X register 
PULX Pull the X register 
LDAD Load accumulator D from memory 
STAD Store accumulator D into memory 

CONVENIENCE MNEMONICS 
BEC,LBEC Branch (short or long) if error clear 
BES,LBES Branch (short or long) if error set 
CLF Clear FIRQ interrupt mask 
CLZ Clear zero condition code bit 
SEF Set FIRQ interrupt mask 
SEZ Set zero condition code bit 

- 24 



TSC 6809 Assembler 

TSC 6809 Assembler 
STANDARD DIRECTIVES OR PSEUDO-OPS 
Besides the standard machine language mnemonics, the TSC assembler 
supports several directives or pseudo-ops. These are instructions for 
the assembler to perform certain operations, and are not directly 
assembled into code. There are three types of directives in this 
assembler, those associated with macros, those associated with 
conditional assembly, and those which generally can be used anywhere 
which we shall call "standard directives". This section is devoted to 
descriptions of these directives which are briefly listed here:

 ORG SETDP 
END PAG 
RMB SPC 
FCB NAM or TTL 
FDB STTL 
FCC ERR 
EQU RPT 
SET LIB 
REG OPT 


Descriptions of each directive and its use follow. 

ORG 

The ORG statement is used to set a new code ’Origin’. This simply means 
that a new address is set into the location Counter (or program counter) 
so that subsequent code will be placed at the new location. The form is 
as follows:

 ORG <expression> 

No label may be placed on an ORG statement and no code is produced. If 
no ORG statement appears in the source, an origin of 0000 is assumed. 

END 

The END pseudo-op is used to signal the assembler that the end of the 
source input has occurred. This terminates whatever pass is currently 
being executed. No label is allowed and no code is generated. An 
expression may be given (as shown below) as the transfer address to be 
placed in a binary file. It is optional, and if supplied when no binary 
file is being produced, will be ignored.

 END [<expression>] 

Note that an end statement is not strictly required, but is the only 
means of getting a transfer address appended to a binary output file. 

- 25 



TSC 6809 Assembler 

TSC 6809 Assembler 

The RMB or Reserve Memory Bytes directive is used to reserve areas of 
memory for data storage. The number of bytes specified by the 
expression in the operand are skipped during assembly. No code is 
produced in those memory location and therefore the contents are 
undefined at run time. The proper useage is shown here:

 [<label>] RMB <expression> 

The label is optional, and the expression is a 16 bit quantity. 

FCB 

The FCB or Form Constant Byte directive is used to set associated memory 
bytes to some value as determined by the operand. FCB may be used to 
set any number of bytes as shown below:

 [<label>] FCB <expr. 1>,<expr. 2>,....<expr. n> 

Where <expr. x> stands for some expression. Each expression given 
(separated by commas) is evaluated to 8 bits and the resulting 
quantities are stored in successive memory locations. The label is 
optional. 

FDB 

The FDB or Form Double Byte directive is used to setup 16 bit quantities 
in memory. It is exactly like the FCB directive except that 16 bit 
quantities are evaluated and stored in memory for each expression given. 
The form of the statement is:

 [<label>] FDB <expr. 1>,<expr. 2>,...,<expr. n> 

Again, the label field is optional. 

FCC 

The FCC or Form Constant Character directive allows the programmer to 
specify a string of ASCII characters delimited by some non-alphanumeric 
character such as a single quote. All the characters in the string will 
be converted to their respective ASCII values and stored in memory, one 
byte per character. Some valid examples follow:

 LABEL1 FCC ’THIS IS AN FCC STRING’ 
LABEL2 FCC .SO IS THIS. 
FCC /LABELS ARE NOT REQUIRED./ 


- 26 



TSC 6809 Assembler 

TSC 6809 Assembler 

 INTRO 
FCC ’THIS STRING HAS CR & LF’,$D,$A 
FCC ’STRING 1’,0,’STRING 2’ 
FCC $04,LABEL,/DELIMITED STRING/ 

Note that more than one delimited string may be placed on a line as in 
the second example. 

EQU 

The EQU or Equate directive is used to equate a symbol to the expression 
given in the operand. No code is generated by this statement. Once a 
symbol has been equated to some value, it may not be changed at a later 
time in the assembly. The form of an equate statement is as follows:

 <label> EQU <expression> 

The label is strictly required in equate statements. 

SET 

The SET directive is used to set a symbol to the value of some 
expression, much as an EQU directive. The difference is that a symbol 
may be SET several times within the source (to different values) while a 
symbol may be Equated only once. If a symbol is SET to several values 
within the source, the current value of the symbol will be the value 
last SET. The statement form is:

 <label> SET <expression> 

The label is strictly required and no code is generated. 

- 27 



TSC 6809 Assembler 

TSC 6809 Assembler 

The REG directive allows the user to setup a list of registers for use 
by the push and pull instructions. This list is represented by a value 
and the value is equated to the label supplied. In this respect, the 
REG directive is similar to the EQU directive. The correct form of the 
REG directive is:

 <label> REG <register list> 

As an example, suppose a program has a large number of occurences of the 
following instructions:

 PSHS A,B,Y,U,DP

 PULS A,B,Y,U,DP 

To make things more convenient and less error prone the REG directive 
could be used as shown here:

 RLIST2 REG A,B,Y,U,DP 

Now all the pushes and pulls referred to above could be accomplished 
with the statements:

 PSHS #RLIST2

 PULS #RLIST2 

Of course, the register list may still be typed out on push and pull 
instructions or an immediate value (with the desired bit pattern) may be 
specified. 

SETDP 

The SETDP or Set Direct Page directive allows the user to set which 
memory page the assembler will use for the direct page addressing mode. 
The correct format is as follows:

 SETDP [<page value>] 

As an example, if "SETDP $D0" is encountered, the assembler will then 
use direct addressing for any address in the range of $D000 to $D0FF. 
It is important to note that this directive does not actually affect the 
contents of the direct page register. The value set is what will be 
used at assembly time to determine direct addressing, but it is up to 
the user to be sure the DP register corresponds at run time. If there 
is no <page value> supplied, direct addressing will be disabled and all 
addresses will be full 16 bit values. Any number of SETDP instructions 
may occur in a program. The default value is page 0 (for 6800 
compatibility). 

- 28 



TSC 6809 Assembler 

TSC 6809 Assembler 

The PAG directive causes a page eject in the output listing and prints a 
header at the top of the new page. Note that the ’PAG’ option must have 
been previously selected in order for this directive to take effect. It 
is possible to assign a new number to the new page by specifying such in 
the operand field. If no page number is specified, the next consecutive 

number will be used. No label is allowed and no code is produced. 
PAG operator itself will not appear in the listing unless some sort 
error is encountered. The proper form is:
The 
of 
PAG [<expression>] 

Where the expression is optional. The first page of a listing does not 
have the header printed on it and is considered to be page 0. The 
intention here is that all options, title, and subtitle may be setup and 
followed by a PAG directive to start the assembled listing at the top of 
page 1 without the option, title, or subtitle instructions being in the 
way. 

SPC 

The SPC or Space directive causes the specified number of spaces (line 
feeds) to be inserted into the output listing. The general form is:

 SPC [<space count>[,<keep count>]] 

The space count can be any number from 0 to 255. If the page option is 
selected, SPC will not cause spacing past the top of a new page. The 
<keep count> is optional and is the number of lines which the user 
wishes to keep together on a page. If there are not enough lines left 
on the current page, a page eject is performed. If there are <keep 
count> lines left on the page (after printing <space count> spaces), 
output will continue on the current page. If the page option is not 
selected, the <keep count> will be ignored. If no operand is given 
(ie. just the directive SPC), the assembler will default to one blank 
line in the output listing. 

TTL OR NAM 

The TTL or NAM directive allows the user to specify a title or name to 
the program being assembled.. This title is then printed in the header 
at the top of each output listing page if the page option is selected. 
If the page option is not selected, this directive is ignored. The 
proper form is:

 TTL <text for the title> 
or 
NAM <text for the title> 

All the text following the TTL or NAM directive (excluding leading 
spaces) is placed in the title buffer. Up to 32 characters are allowed 
with any excess being ignored. It is possible to have any number of TTL 

- 29 



TSC 6809 Assembler 

TSC 6809 Assembler 

STTL 

The STTL or Subtitle directive is used to specify a subtitle to be 
printed just below the header at the top of an output listing page. It 
is specified much as the TTL directive:

 STTL <text for the subtitle> 

The subtitle may be up to 52 characters in length. If the page option 
is not selected, this directive will be ignored. As with the TTL 
option, any number of STTL directives may appear in a source program. 
The subtitle can be disabled or turned off by an STTL command with no 
text following. 

ERR 

The ERR directive may be used to insert user-defined error messages in 
the output listing. The error count is also bumped by one. The proper 
form is:

 ERR <message to be printed> 

All text past the ERR directive (excluding leading spaces) is printed as 
an error message (it will be preceded by three asterisks) in the output 
listing. Note that the ERR directive line itself is not printed. A 
common use for the ERR directive is in conjunction with conditional 
assembly such that some user-defined illegal condition may be reported 
as an error. 

RPT 

The RPT or Repeat directive causes the succeeding line of source to be 
repeated some specified number of times. The syntax is as follows:

 RPT <count> 

where <count> may be any number from 1 to 127. For example, the 
following two lines:

 RPT 4 
ASLB 


- 30 



TSC 6809 Assembler 

TSC 6809 Assembler 

 ASLB 
ASLB 
ASLB 
ASLB 


Some directives, such as IF or MACRO, may not be repeated with the RPT 
command. These cases are where it is illogical or impractical to do so. 
If attempted, the RPT will simply be ignored. 

LIB 

The LIB or Library directive allows the user to specify an external file 
for inclusion in the assembled source output. Under normal conditions, 
the assembler reads all input from the file specified on the calling 
line. The LIB directive allows the user to temporarily obtain the source 
lines from some other file. When all the lines in that external file 
have been read and assembled, the assembler resumes reading of the 
original source file. The proper syntax is:

 LIB <file spec> 

where <file spec> is a standard FLEX file specification. The default 
drive is the assigned working drive and the default extension is .TXT. 
Any END statements found in the file called by the LIB directive are 
ignored. The LIB directive line itself does not appear in the output 
listing. Any number of LIB instructions may appear in a source listing. 
It is also possible to nest LIB files up to 12 levels. Nesting refers 
to the process of placing a LIB directive within the source that is 
called up by another LIB directive. In other words, one LIB file may 
call another. 

OPT 

The OPT or Option directive allows the user to choose from several 
different assembly options which are available to him. These options 
are generally related to the format of the output listing and object 
code. The options which may be set with this command are listed below. 
There are several options not listed here which may be set from the FLEX 
command line. See the appropriate section earlier in the manual for 
these options. The proper form of this instruction is:

 OPT <option 1>,<option 2>,...,<option n> 

Note that any number of options may be given on one line if separated by 
commas. No label is allowed and no spaces may be imbedded in the option 
list. The options are all set during pass one only although the 
instruction is parsed in pass two as well for error reporting purposes. 
If contradicting options are specified, the last one appearing takes 
precedence. If a particular option is not specified, the default case 
for that option takes effect. The default cases are signified below by 
an asterisk. 

- 31 



TSC 6809 Assembler 

TSC 6809 Assembler 

 PAG enable page formatting and numbering 
NOP* disable pagination

 CON print conditionally skipped code 
NOC* suppress conditional code printing

 MAC* print macro calling lines 
NOM suppress printing of macro calls

 EXP print macro expansion lines 
NOE* Suppress macro expansion printing

 * denotes default option and is not part of option name 
- 32 



TSC 6809 Assembler 

TSC 6809 Assembler 
CONDITIONAL ASSEMBLY 
This assembler supports "conditional assembly" or the ability to 
assemble only certain portions of your source program depending on the 
conditions at assembly time. Conditional assembly is particularly 
useful in situations where you might need several versions of a program 
with only slight changes between versions. 

As an example, suppose we required a different version of some program 
for 4 different systems whose output routines varied. Rather than 
prepare four different source listings, we could prepare one which would 
assemble a different set of output routines depending on some variable 
which was set with an EQU directive near the beginning of the source. 
Then it would only be necessary to change that one EQU statement to 
produce any of the four final programs. This would make the software 
easier to maintain, as besides only needing to keep track of one copy of 
the source, if a change is required in the body of the program, only one 
edit is required to update all versions. 

THE IF-ENDIF CLAUSE 

In its simplest form, conditional assembly is performed with two 
directives: IF and ENDIF. The two directives are placed in the source 
listing in the above order with any number of lines of source between. 
When the assembler comes across the IF statement, it evaluates the 
expression associated with it (we will discuss this expression in a 
moment) and if the result is true, assembles all the lines between the 
IF and ENDIF and then continues assembling the lines after the ENDIF. 
If the result of the expression is false, the assembler will skip all 
lines between the IF and ENDIF and resume assembly of the lines after 
the ENDIF. The proper syntax of these directives is as follows:

 IF <expression>

 .

 . conditional code goes here

 .

 ENDIF 

The ENDIF requires no additional information but the IF requires an 
expression. This expression is considered FALSE if the 16-bit result is 
equal to zero. If not equal to zero, the expression is considered TRUE. 

A more powerful conditional assembly construct is possible with the ELSE 
directive. The ELSE directive may be placed between the IF and ENDIF 
statements. Its effect is to switch the sense of the test for the lines 
between it and the ENDIF. In effect, the lines of source between the IF 
and ENDIF are split into two groups by the ELSE statement. Those lines 
before the ELSE are assembled if the expression is true while those 
after (up to the ENDIF) are ignored. If the expression is false, the 
lines before the ELSE are ignored while those after it are assembled. 
The IF-THEN-ELSE construct appears as follows: 

- 33 



TSC 6809 Assembler 

TSC 6809 Assembler 

 ELSE 
. 
. this code assembled if expression is false 
.

 ENDIF 

The ELSE statement does not require an operand and there may be only one 
ELSE between an IF-ENDIF pair. 

It is possible to nest IF-ENDIF clauses (including ELSE’s). That is to 
say, an IF-ENDIF clause may be part of the lines of source found inside 
another IF-ENDIF clause. You must be careful, however, to terminate the 
inner clause before the outer. 

There is another form of the conditional directive, namely IFN which 
stands for "IF Not". This directive functions just like IF except that 
the sense of the test is reversed. Thus the code immediately following 
is assembled if the result of the expression is NOT TRUE. An 
IFN-ELSE-ENDIF clause appears as follows:

 IFN <expression> 
. 
. this code assembled if expression is FALSE 
.

 ELSE 
. 
. this code assembled if expression is TRUE 
.

 ENDIF 

THE IFC-ENDIF CLAUSE 

Another form of conditional assembly is very similar to the IF-ENDIF 
clause defined above, but depends on a comparison of two strings for its 
conditionality instead of a true-false expression. This type of 
conditional assembly is done with the IFC and IFNC directives (for "IF 
Compare" and "IF Not Compare") as well as the ELSE and ENDIF discussed 
above. Thus for the IFC directive we have a clause like:

 IFC <string 1>,<string 2> 
. 
. this code assembled if strings are equal 
.

 ELSE 
. 
. this code assembled if strings are not equal 
.

 ENDIF 

- 34 



TSC 6809 Assembler 

TSC 6809 Assembler 

A common application of this type of conditional assembly is in macros 
(defined in the next section) where one or both of the strings might be 
a parameter passed into the macro. 

THE IF-SKIP CLAUSE 

The IF-skip type of conditional assembly is a method which does not use 
(in fact does not allow) a related ENDIF or ELSE. Instead, the 
assembler is caused to skip a specified number of lines of source 
depending on the result of the expression or string comparison. 

IMPORTANT NOTE: 
This type of conditional assembly is 
ONLY allowed within the body of a macro. 
Any use of it outside a macro will 
result in an error. Macros are defined 
in the next section. 

As before, the possible directives are: IF, IFN, IFC, and IFNC. This 
type of conditional assembly is performed with a single instruction. 
Instead of code being assembled on a true result, the specified number 
of lines are SKIPPED. This number of lines can be in a forward or 
reverse direction. The syntax is as shown:

 IF <expression>,<skip count>

 or

 IFC <string 1>,<string 2>,<skip count> 

The skip count must be a decimal number between 1 and 255. It may be 
preceded by a plus or minus sign. A positive number produces a forward 
skip while a negative number produces a backwards skip. A skip count of 
zero has no effect (the instruction following the IF directive will be 
executed next). A skip count of one will cause the second line after 
the IF statement to be the next one executed (the one line directly 
following the IF statement is ignored). A skip count of negative one 
will cause the line just before the skip count to be the next one 
executed. The assembler will not skip past the end or beginning of the 
macro which contains the IF-skip statement. If a skip count is 
specified which is beyond these limits, the assembler will be left 

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TSC 6809 Assembler 

TSC 6809 Assembler 

IMPORTANT NOTE 

In order for conditionals to function properly, they must capable of 
evaluation in pass one so that the same result will occur in pass two. 
Thus if labels are used in a conditional expression, they must have been 
defined in the source before the conditional directive is encountered. 

- 36 



TSC 6809 Assembler 

TSC 6809 Assembler 
MACROS 
A macro is a facility for substituting a whole set of instructions and 
parameters in place of a single instruction or call to the macro. There 
are always two steps to the use of macros, the definition and the call. 
In the definition we specify what set of instructions make up the body 
of the macro and assign a name to it. This macro may then be called by 
name with a single assembler instruction line. This single line is 
replaced by the body of the macro or the group of lines which were 
defined as the macro. This replacement of the calling line with the 
macro body is called the macro "expansion". It is also possible to 
provide a set of parameters with the call which will be substituted into 
the desired areas of the macro body. 

A simple example will assist in the understanding of macros. Let us 
define a macro which will shift the ’D’ register left four places. This 
is such a simple operation that it does not really require or make 
effective use of macros, but it will suffice for learning purposes. In 
actuality this routine would probably be written in-line or, if required 
often, written as a subroutine. 

The first step is to define the macro. This must be done BEFORE THE 
FIRST CALL to the macro. It is good practice to define all macros early 
in a program. The definition is initiated with a MACRO directive and 
terminated by an ENDM directive. The definition of our example would be 
as follows:

 ASLD4 MACRO

 ASLB

 ROLA

 ASLB

 ROLA

 ASLB

 ROLA

 ASLB

 ROLA

 ENDM 

The first line is the MACRO directive. Note that the name of the macro 
is specified with this directive by placing it in the label field. This 
macro name should follow all the rules for labels. It will NOT be 
placed in the symbol table, but rather in a macro name table. The body 
of the macro follows and is simply lines of standard assembly source 
which shift the ’D’ register left four places. The definition is 
terminated by the ENDM directive. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

At this point we may continue with our assembly program and when we 
desire to have the ’D’ register shifted left four places, simply call 
the macro as follows:

 .

 .

 LDA VALUE

 LDB VALUE+1

 ASLD4 here is the macro call

 STD RESULT

 .

 . 

You can see that calling a macro consists of simply placing its name in 
the mnemonic field of a source line. When the assembler sees the above 
call, it realizes that the instruction is not a standard 6809 mnemonic, 
but rather a macro that has been previously defined. The assembler will 
then replace the ASLD4 with the lines which make up the body of that 
macro or "expand" the macro. The result would be the following 
assembled code:

 .

 .

 LDA VALUE

 LDB VALUE+1

 ASLB the body of the macro

 ROLA replaces the call

 ASLB

 ROLA

 ASLB

 ROLA

 ASLB

 ROLA

 STD RESULT

 .

 . 

You should note that a macro call differs from a subroutine call in that 
the macro call results in lines of code being placed in-line in the 
program where a subroutine call results in the execution of the routine 
at run-time. Five calls to a subroutine still only requires one copy of 
the subroutine while five calls to a macro results in five copies of the 
macro body being inserted into the program. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

If macros were limited to what was described above, they would probably 
not be worth the space it took to implement them in the assembler. The 
real power of macros comes in "parameter substitution". By that we mean 
the ability to pass parameters into the macro body from the calling 
line. In this manner, each expansion of a macro can be different. 

As an example, suppose we wanted to add three 16-bit numbers found in 
memory and store the result in another memory location. A simple macro 
to do this (we shall call it ADD3) would look like this:

 ADD3 MACRO

 LDD LOC1 get first value in ’D’

 ADDD LOC2 add in second value

 ADDD LOC3 add in third value

 STD RESULT store result

 ENDM 

Now let’s assume we need to add three numbers like this in several 
places in the program, but the locations from which the numbers come and 
are to be stored are different. We need a method of passing these 
locations into the macro each time it is called and expanded. That is 
the function of parameter substitution. The assembler lets you place up 
to nine parameters on the calling line which can be substituted into the 
expanded macro. The proper form for this is:

 MACNAM <prm.l>,<prm.2>,<prm.3>,...,<prm.9> 

where "MACNAM" is the name of the macro being called. Each parameter 
may be one of two types: a string of characters enclosed by like 
delimiters and a string of characters not enclosed by delimiters which 
contains no embedded spaces or commas. The delimiter for the first type 
may be either a single quote (’) or a double quote (") but the starting 
and ending delimiter of a particular string must be the same. A comma 
is used to separate the parameters. These parameters are now passed 
into the macro expansion by substituting them for 2-character "dummy 
parameters" which have been placed in the macro body on definition. 
These 2-character dummy parameters are made up of an ampersand (&) 
followed by a single digit representing the number of the parameter on 
the calling line as seen above. Thus any occurence of the dummy 
parameter, "&1", would be replaced by the first parameter found on the 
calling line. 

Let’s re-do our ADD3 macro to demonstrate this process. The definition 
of ADD3 now looks like this:

 ADD3 MACRO

 LDD &l get first value in ’D’

 ADDD &2 add in second value

 ADDD &3 add in third value

 STD &4 store result

 ENDM 

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TSC 6809 Assembler 

TSC 6809 Assembler 

would be replaced with LOC2, etc. 
appear as follows:
The resulting assembled code would 
LDD 
ADDD 
ADDD 
STD 
LOC1 
LOC2 
LOC3 
RESULT 
get first value in ’D’add in second valueadd in third valuestore result 
Another call to the macro might be: 
ADD3 ACE,TWO,LOC3,LOC1 
which would result in the following expansion: 
LDD 
ADDD 
ADDD 
STD 
ACE 
TWO 
LOC3 
LOC1 
get first value in ’D’add in second valueadd in third valuestore result 
Now you should begin to see the power of macros. 
There is actually a tenth parameter which may be passed into a macro 

represented by the dummy parameter "&0". It is presented on the calling 
line as so:

 <prm.0> MACNAM <prm.l>,<prm.2>,<prm.3>,...,<prm.9> 

This parameter is somewhat different from the others in that it must be 
a string of characters that conform to the rules for any other assembly 
language label since it is found in the label field. It is in fact a 
standard label which goes into the symbol table and can be used in other 
statement’s operands like any other label. 

Ignoring a Dummy Parameter 

There may be times when a programmer wishes to have an ampersand 
followed by a number in a macro which is not a dummy parameter and 
should therefore not be replaced with a parameter string. An example 
would be an expression where the value of MASK was to be logically 
’anded’ with the number 4. The expression would appear like:

 MASK&4 

If this expression were in a macro, upon expansion the &4 would be 
replaced with the fourth parameter on the calling line. It is possible 
to prevent this, however, by preceding the ampersand with a backslash 
(\) like this: 

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TSC 6809 Assembler 

TSC 6809 Assembler 

When the assembler expands the macro containing this expression, it will 
recognize the backslash, remove it, and leave the ampersand and 
following number intact. 

Another case where this can be useful is when a macro is defined within 
a macro (that is possible!) and you wish to place dummy parameters in 
the inner macro. 

THE EXITM DIRECTIVE 

Sometimes it is desireable to exit a macro prematurely. The EXITM 
directive permits just that. During expansion of a macro, when an EXITM 
command is encountered the assembler immediately skips to the ENDM 
statement and terminates the expansion. This probably does not seem 
logical , and is not except when used with conditional assembly. 

To portray the use of EXITM, assume we have some macro called XYZ which 
has two parts. The first part should always be expanded, but the second 
should only be expanded in certain cases. We could use EXITM and the 
IFNC directives to accomplish this as follows:

 XYZ MACRO 
. 
. code that should always be generated 
.


 IFNC &2,YES 
EXITM 
ENDIF


 . 
. code that is only sometimes generated 
.

 ENDM 

The following calls would result in the second part being expanded or 
producing code:

 XYZ "PARAMETER 1",YES 
XYZ "PARAMETER 1","YES" 
XYZ 0,YES 


while all of the following would result in the second part not being 
expanded:

 XYZ "PARAMETER 1",NO 
XYZ JUNK,NO 
XYZ JUNK 
XYZ PRMI,PRM2 


The EXITM directive itself requires no operand. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

There is another type of assembler construct which may only be used 
inside of a macro, called the DUP-ENDD clause. The assembler will 
duplicate the lines placed between the DUP and ENDD (end dup) 
instructions some specified number of times. The proper form is:

 DUP <dup count> 
. 
. code to be duplicated 
.


 ENDD 

where the <dup count> is the number of times the code should be 
duplicated. The <dup count> may be any valid expression, but must be in 
the range of 1 to 255 decimal. Note that DUP-ENDD clauses may NOT be 
nested. That is to say, one DUP-ENDD clause may not be placed inside 
another. 

As an example, let’s take our first example in this section on macros 
and spruce it up a little. Assume we want a macro that will shift the 
’D’ register to the left ’x’ places where ’x’ can vary in different 
calls to the macro. The DUP-ENDD construct will work nicely for this 
purpose as seen here:

 ASLDX 
MACRO 
DUP &l 
ASLB 
ROLA 
ENDD 
ENDM 


Now to shift the ’D’ register left four places we call the macro with:

 ASLDX 4 

To shift it left 12 places we simply use the instruction:

 ASLDX 12 

And so on. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

A few more hints on using macros may be of value. 

One important thing to remember is that parameter substitution is merely 
replacing one string (the dummy parameter or &x) with another (the 
parameter string on the calling line). You are not passing a value into 
a macro when you have a parameter of "1000", but rather a string of four 
characters. When the expanded source code of the macro is assembled, 
the string may be considered a value, but in the phase of parameter 
substitution it is merely a string of characters. An example macro will 
help clarify this point.

 TEST MACRO

 LDA #$&l COMMENT FIELD IS HERE

 LDB L&l

 NOP PARAMETERS CAN EVEN BE

 NOP SUBSTITUTED INTO

 NOP COMMENTS &2

 &3 OR THEY CAN BE A MNEMONIC

 &4 TST M&1M OR LABEL OR INSIDE A STRING

 ENDM 

Now if this macro were called with the following command:

 TEST 1000,’LIKE THIS’,SEX,"LABEL" 

The expanded source code would look like this:

 LDA #$1000 COMMENT FIELD IS HERE

 LDB L1000

 NOP PARAMETERS CAN EVEN BE

 NOP SUBSTITUTED INTO

 NOP COMMENTS LIKE THIS

 SEX OR THEY CAN BE A MNEMONIC

 LABEL TST M1000M OR LABEL OR INSIDE A STRING 

Note that in the LDA instruction the parameter "1000" is used as a 
number but in the LDB and TST instructions it is part of a label. The 
second parameter is not even substituted into the actual program, but 
rather into the comment field. The use of parameter number one in the 
TST instructions shows that the dummy parameter does not have to be a 
stand alone item but can be anywhere in the line. 

Another convenient method of using macros is in conjunction with the 
IF-skip type of conditional directive. With a negative or backward skip 
we can cause a macro to loop back on itself during expansion. A good 
example of this would be a case where the programmer must initialize one 
hundred consecutive memory locations to the numbers one through one 
hundred. This would be a very tedious task if all these numbers had to 
be setup by FCB directives. Instead we can use a single FCB directive, 
the IF-skip type of directive, and the SET directive to accomplish this 
task. 

- 43 



TSC 6809 Assembler 

TSC 6809 Assembler 
MACRO 
COUNT SET 0 INITIALIZE COUNTER 
COUNT SET COUNT+1 BUMP BY ONE 
FCB COUNT SET THE MEMORY BYTE 
IF COUNT<100,-2 
ENDM 

If you try this macro out, you will see that it expands into quite a bit 
of source if the macro expansions are being listed because the 3rd, 4th 
and 5th line are expanded for each of the one hundred times through. 
However, only one hundred bytes of object code are actually produced 
since lines 3 and 5 don’t produce code. 

This assembler does not allow local variables. If a label is specified 
on a line in the macro, you will receive a multiply defined symbol error 
if the macro is called more than once. There is a way to get around 
this shortcoming that is somewhat crude, but effective. That is to use 
a dummy parameter as a label and require the programmer to supply a 
different label name as that parameter each time the macro is called. 
For example, consider the following example:

 SHIFT MACRO 
PSHS D 
LDA &l 
LDB #&2

 &3 
ROLA 
DECB 
BNE &3 
STA &l 
PULS D 
ENDMv 

Now if this macro was called with the line:

 SHIFT FLAG,3,CALL1 

The resulting macro expansion would look like:

 PSHS D 
LDA FLAG 
LDB #3

 CALL1 ROLA 
DECB 
BNE CALL1 
STA FLAG 
PULS D 

There is no problem here, but if the macro were called again with the 
same string for parameter 3 (CALL1), a multiply defined symbol error 
would result. Thus any subsequent calls to SHIFT must have a unique 
string for parameter 3 such as CALL2, CALL3, etc. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

1) A macro must be defined before the first call to it. 

2) Macros can be nested both in calls and in definitions. That is, one 
macro may call another and one macro may be defined inside another. 

3) Comment lines are stripped out of macros when defined to save storage 
space in the macro text buffer. 

4) Local labels are not supported. 

5) A macro cannot call a LIBrary file. That is, a LIB directive cannot 
appear within a macro. 

6) No counting of parameters is done to be sure enough parameters are 
supplied on the calling line to satisfy all dummy parameters in the 
defined macro. If the body of a macro contains a dummy parameter for 
which no parameter is supplied on the calling line, the dummy 
parameter will be replaced with a null string or effectively removed. 

7) The macro name table is searched before the mnemonic table. This 
means that a standard mnemonic or directive can be effectively 
redefined by replacing it with a macro of the same name. 

8) Once a macro has been defined, it cannot be purged nor re-defined. 

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TSC 6809 Assembler 

TSC 6809 Assembler 
SPECIAL FEATURES 
This section covers a few special features of the 6809 Mnemonic 
Assembler that don’t seem to fit under any other specific category. 

END OF ASSEMBLY INFORMATION 

Upon termination of an assembly, and before the symbol table is output, 
three items of information may be printed: the total number of errors 
encountered, the total number of warnings encountered, and the address 
of the last byte of code assembled. 

The number of errors is always printed in the following manner:

 0 ERROR(S) DETECTED 

The number of warnings are printed only if warnings have not been 
suppressed by the ’W’ option on the command line and if the number is 
greater than zero (ie. only if there was a warning):

 0 ERROR(S) DETECTED 2 WARNING(S) REPORTED 

The last assembled address is printed only if the assembled output 
listing is turned off by the ’L’ option on the command line. It is 
actually the last address which the assembler’s program counter register 
was pointing to, so there may not really be an assembled byte of code at 
this address. For example if the last instruction in a program except 
for the END was an RMB directive, the address would be the last byte 
reserved by that command. This information is presented as follows:

 LAST ASSEMBLED ADDRESS: 1055 

The address is printed as a 4-digit hexadecimal value. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

A mechanism has been included in the assembler to inform the programmer 
when a long branch or jump could be replaced by a short branch. The 
purpose is to allow size and speed optimization of the final code. This 
indicator is a greater-than sign placed just before the address of the 
long branch or jump instruction which could be shortened. The following 
section of code shows just how it looks:

 3420 B6 E004 
3423 84 01 
>3425 1027 FFF7 
3429 B6 E005 
342C 81 20 
342E 24 06 
>3430 BD 3436 
>3433 7E 3420 
3436 34 04 
INCH 
OUTCH 
LDA 
ANDA 
LBEQ 
LDA 
CMPA 
BHS 
JSR 
JMP 
PSHS 
$E004#$01INCH$E005#$20OUTCHOUTCHINCHB 
. 
. 
. 

These indicator flags may be suppressed by selecting the ’W’ option in 
the command line option list. 

AUTO FIELDING 

The assembler automatically places the four fields of a source line 
(label, mnemonic, operand, and comment) in columns in the output 
assembled listing. This allows the programmer to edit a condensed 
source file without impairing the readability of the assembled listing. 
The common method of doing this is to separate the fields by only one 
space when editing. The assembled output places all mnemonics beginning 
in column 8, all opcodes beginning in column 15, and all comments 
beginning in column 25 assuming the previous field does not extend into 
the current one. There are a few cases where this automatic fielding 
can break down such as lines with errors, but these cases are rare and 
generally cause no problem. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

The assemble automatically sets up all necessary tables and buffers 
depending on the amount of memory contained in your system. The amount 
of memory contained is determined by reading the memory end value 
(MEMEND) in FLEX. The tables or buffers which can vary in size are as 
follows: 

SYMBOL TABLE 
This table is where all symbols are maintained during 
assembly. Each entry into the symbol table requires 8 bytes, 6 
for the name and two for the address or value associated with 
it. This assembler uses a hashed symbol table technique which 
can mean that symbols are pseudo-randomly scattered throughout 
the table. This method is very fast but has one drawback the 
assembler is usually not able to completely fill all 
positions in the table. Thus a symbol table full error 
message does not necessarily mean that every position in the 
table is really full. It simply means the assembler was 
unable to put any more symbols in the table due to the hashing 
technique used. The larger the table, the faster the hashing 
method will execute and accordingly, the faster the assembler 
will run. If possible, it is good to have 50% more space in 
the symbol table than will be required to actually hold the 
number of symbols in a program. 

SOURCE BUFFER 
This is the buffer which holds the source program to be 
assembled. To gain speed, the assembler reads as many lines as 
it can into this buffer all at once. The assembly operation 
is carried out on each buffer individually. This buffer may 
be any size so long as it will hold the longest line that may 
be encountered in the source. There must also be a reserved 
256-byte overflow area directly following the end of the 
source buffer. 

MACRO TEXT BUFFER 
This is the buffer where macros are stored upon definition. 
If few macros are to be used, it can be very small. The more 
macros anticipated, the larger the buffer should be. 

MACRO NAME TABLE 
This is a table where macro names and locations are stored. 
Each entry requires 8 bytes, 6 for the macro name and 2 for 
the address of the macro body in the macro text buffer. 
Again, if few macros are to be defined, this table can be 
quite small. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

The assembler attempts to provide a general sizing of these tables for 
any size system in which it is run. This sizing is done according to 
the following approximate formulae:

 Let AVM = MEMEND - MEMBEG

 where AVM implies available memory 
MEMEND refers to the end of memory as in FLEX 
MEMBEG is the start of the RAM buffer area

 Then

 SYMBOL TABLE = (AVM-1K)*0.625 
MACRO TEXT BUFFER = (AVM-1K)*0.188 
MACRO NAME TABLE = (AVM-1K)*0.031 
MACRO ACTIVATION BUFFER = (AVM-1K)*0.031 
SOURCE BUFFER = AVM-256-(sum of above spaces) 


These formulae change if there is enough memory to produce a symbol 
table of larger than 16K according to the symbol table formula given 
above. In that case, the symbol is limited to 16K (enough for almost 
2000 symbols) and the remaining space is divided equally between the 
macro text buffer and the source buffer. 

These table sizes can be set manually by the programmer if so desired. 
See the section on adapting to your system for details. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

In the section on using the assembler at the beginning of this manual, 
command line parameters are discussed. That section describes how to 
place a parameter on the command line for passing into the source, but 
it does not elaborate on how the programmer tells the assembler where in 
the source to substitute those parameters. If you have read the section 
on macros, you should already understand the concept of parameter 
substitution. If not, read that section before continuing here. 

Much as in macro parameter substitution, there are 2-character symbols 
or dummy parameters which, if placed anywhere in the source, will be 
replaced by the parameters supplied on the command line. In macros, the 
parameters from the macro calling line were substituted into the macro 
body during expansion of the macro. Here, the parameters from the 
command line are substituted into the source as it is read in from the 
disk. In macros, there were 10 possible parameters. Here there are 
three possible. The 2-character dummy parameters for these three are 
’&A’, ’&B’, and ’&C’. These correspond to the three possible command 
line parameters represented here:

 +++ASMB,<filename>,+<options>,+<prm.A>,<prm.B>,<prm.C> 

As can be seen, the three parameters are separated by commas. 
Just as in macros, the dummy parameters can be ignored by placing a 
backslash directly in front of the ampersand. Thus the following line 
of edited source:


 VALUE EQU MASK\&COUNT 

would be read into the assembler as:

 VALUE EQU MASK&COUNT 

A quick example should help clarify the preceding descriptions. The 
following program contains one dummy parameter, ’&A’.

 * ROUTINE TO OUTPUT TO ONE OF TWO PORTS 
OPT PAG,CON 
TTL OUTPUT ROUTINE FOR PORT #&A 
PAG 
IFN (&A=0)|(&A=l) 
ERR NOT A VALID PORT NUMBER 
ELSE 
IF &A=0 
ACIA EQU $E000 
ELSE 
ACIA EQU $E004 
ENDIF 
ENDIF 

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TSC 6809 Assembler 

TSC 6809 Assembler 

 END 

Now if this file were assembled with a command line like:

 +++ASMB,FILE,+BGDS,+1 

(assuming the file is very creatively called, ’FILE’), we would see the 

following assembled output: 
OUTPUT ROUTINE FOR PORT #l TSC ASSEMBLER PAGE 1 
IFN (1=0)1(1=1) 
ERR NOT A VALID PORT NUMBER 
ELSE 
IF l=0 
ACIA EQU $E000 
ELSE 
E004 ACIA EQU $E004 
ENDIF 
ENDIF 
0000 F6 E004 OUTCH LDB ACIA 
0003 C4 02 ANDB #$02 
0005 27 F9 BEQ OUTCH 
0007 B7 E004 STA ACIA 
000A 39 RTS 
END

 0 ERROR(S) DETECTED 
Note that the first page of output is not shown. 


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TSC 6809 Assembler 

TSC 6809 Assembler 
OBJECT CODE PRODUCTION 
The assembler is capable of producing two kinds of object code output. 
One is a binary file in the standard FLEX binary file format. The first 
section of this manual explains how to produce such a file and how to 
assign a name to it. The second type is a direct output to tape. This 
object code is produced in the standard Motorola ’51-S9’ tape format. 
This is an ASCII hex record format as shown:

 S1BBAAAADDDDDDDDDD......DDDDCC

 where

 S1 is a record start marker

 BB is a byte count which includes all bytes

 in the record past the byte count itself

 AAAA is the load address of the first data byte

 DD is the actual data

 CC is a checksum equivalent to the one’s

 complement of the modulo 256 sum of all

 bytes preceding the checksum (except the S1) 

This data is output, character at a time, through a jump vector located 
near the beginning of the assembler. As supplied this jump vector is 
pointing to the PUTCHR or output character routine of FLEX. If your 
tape device is located on the same port as your terminal, this should be 
satisfactory. If, however, you have a tape device located elsewhere, 
you will need to patch this jump vector to point to a routine you must 
supply to output a character to your tape device and then return. 
Directions for patching this address can be found in the section on 
adapting to your system. 

Note that this data is output periodically during an assembly. If your 
tape device is on the same port as your terminal you will want to turn 
off the listing and symbol table printing options so that only the 
object code data is output to your tape. 

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TSC 6809 Assembler 

TSC 6809 Assembler 
ERROR AND WARNING MESSAGES 
The assembler supports warning messages and two types of error messages: 
fatal and non-fatal. A fatal error is one which will cause an immediate 
termination of the assembly such as not enough memory. A non-fatal 
error results in an error message being inserted into the listing and 
some sort of default code being assembled if the error is in a code 
producing line. The assembly is allowed to continue on non-fatal 
errors. Warning messages are handled much like non-fatal errors: the 
message is inserted in the output listing and the assembly is allowed to 
continue. These warning messages may be suppressed by the ’W’ option in 
the command line. Error messages may not be suppressed. 

All messages are output as English statements - not as error numbers. 
These messages announce violations of any of the rules and restrictions 
set forth in this manual and are, therefore, essentially 
self-explanatory. Error messages are output with three asterisks 
preceding the message. Warning-messages are output with two asterisks 
preceding the message. This can be used to quick locate the messages 
either by, eye or with an editor. 

Possible NON-FATAL error messages are as follows:

 UNDEFINED SYMBOL 
MULTIPLY DEFINED SYMBOL 
UNRECOGNIZABLE MNEMONIC OR MACRO 
ILLEGAL LABEL 
ILLEGAL OPERAND 
RELATIVE BRANCH TOO LONG 
SYNTAX ERROR 
ILLEGAL INDEXED MODE 
ILLEGAL CONSTANT 
ILLEGAL OPTION 
OPERAND OVERFLOW! 
OVERFLOW! 
UNBALANCED CLAUSE 
UNDEFINED IN PASS 1 
NOT ALLOWED IN THIS CONTEXT 
MACRO EXISTS 
PHASING ERROR DETECTED 


A couple of these could use some elaboration. The OPERAND OVERFLOW 
message results from attempting to generate too much data from a single 
FCB, FDB, or FCC instruction. A maximum of 256 bytes of data can be 
generated by a single instruction of that type. An example of the 
OVERFLOW error is when LIB files are nested more than 12 levels deep. 
The UNBALANCED CLAUSE message results when one directive of a clause is 
missing such as an ENDIF with no IF. The NOT ALLOWED IN THIS CONTEXT 
message is generally associated with macros, ie. when an operation is 
attempted that is illegal inside a macro or vice versa. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

 ILLEGAL FILE NAME 
NO SUCH FILE 
ILLEGAL OPTION SPECIFIED 
INSUFFICIENT MEMORY 
MACRO OVERFLOW! 


The first three are associated with errors in the command line. The 
INSUFFICIENT MEMORY message is issued when automatic table setup is 
enabled and there is not at least 3K of buffer area. The MACRO OVERFLOW 
message occurs when any of the macro buffers is overflowed. 

Possible warning messages are as follows:

 FORCED ADDRESS TRUNCATED 
IMMEDIATE VALUE TRUNCATED 
ILLOGICAL FORCING IGNORED 


The first warning is printed if an address is forced to 8 bits (with the 
’<’ character) and must be truncated to fit. The second occurs on lines 
where an immediate value must be truncated to fit in 8 bits. For 
example, ’ LDB #$42E5’ would result in such a warning. The third is 
issued if address length forcing (with the ’<’ or the ’>’) is done in an 
operand where not possible. For example, the instruction ’ LDB 
<[BUFCNT]]’ would result in such a warning. 

As stated in a previous section, the total number of errors is reported 
at the end of the assembly and if warning messages are enabled, the 
number of warnings are also output. 

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TSC 6809 Assembler 

TSC 6809 Assembler 
ADAPTING TO YOUR SYSTEM 
In general, if you have FLEX up and running and have at least 16K of 
user memory, there will be no need for any adapting whatsoever. Some 
users, however, always feel the need to modify certain things and this 
section describes how to make all the changes which we felt might be 
desired (and which would be feasible). With the exception of MEMEND, 
these changes must all be made to the object code of the assembler. 
This can be done by loading the assembler (with a GET ASMB.CMD command), 
making the desired changes in memory, and saving the result on disk 
(with the SAVE command). 

MEMEND 
If using the automatic table setup which the assembler 
performs for you, the MEMEND value in FLEX should be set to 
the last address which the assembler should use. FLEX 
initializes MEMEND to the actual end of user memory. You may 
have an application where you don’t want this to be the case. 
If so, set MEMEND manually before executing the assembler. 

EXIT ADDRESS

 When the assembler is finished, it jumps into FLEX’s warm 
start. If you wish it to exit to some other address, place 
that address at location $0027. 

OUTPUT CHARACTER ROUTINE

 As supplied, the assembler outputs through FLEX’s PUTCHR 
routine. This takes advantage of the escape-return sequence in 
FLEX to pause or terminate an output listing. If, however, 
you wish to output through some user supplied output routine, 
place the address of such a routine at location $002A. This 
routine should output the character in the A register and 
return without affecting any registers except the condition 
codes. 

TAPE OUTPUT CHARACTER ROUTINE

 Presently, tape output is performed character at a time 
through the PUTCHR routine in FLEX. This causes any tape 
output to be routed to the terminal which may be the same port 
on which the tape device is located. If you require a 
different output routine for tape, place the address of such a 
routine at location $002D. This routine should output the 
character in the A register to the tape device and return 
without affecting any registers except the condition codes. 

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TSC 6809 Assembler 

TSC 6809 Assembler 

 If the page mode is selected, the assembler automatically 
places a header at the top of each page (with the current page 
number) and performs a page eject at the bottom. The number 
of lines which are output before the page eject occurs 
(including the header lines) is set at location $0018 in the 
assembler. This value is currently set to 58 lines. Change if 
desired. 

LABELS PER LINE

 The symbol table output is done with multiple symbols per 
line. Currently there are 5 labels per line. If desired, this 
number can be changed by setting the byte at location $0019. 

AUTO FIELDING COLUMNS

 As explained in the special features section, this assembler 
performs auto fielding. The columns in which the fields are 
placed are currently set to 8, 15, and 25 for the mnemonic, 
operand, and comment fields respectively. If desired, these 
columns can be changed by altering the three bytes beginning 
at location $001A. 

TAPE CONTROL

 When tape output is selected, the assembler turns on the tape 
unit, delays for a set period, then begins the output. When 
the last data has been output, the assembler turns the tape 
unit off. This tape on and off control is performed by 
outputting up to four characters for each function (on and 
off). Currently these characters are all set to nulls ($00) as 
the assembler expects manual tape control. If you wish to set 
these characters, the four tape on characters should be placed 
at locations $001E through $0021. The four tape off charcters 
should be placed at locations $0022 through $0025.

 The time delay for tape turn-on can also be adjusted by 
altering the byte at location $001D. This byte is currently 
set to 4 (roughly 2 seconds) and should be raised for longer 
delays or lowered for shorter delays (can be zero for no 
delay). 

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TSC 6809 Assembler 

TSC 6809 Assembler 

 If you wish to set up the necessary tables and buffers 
manually, you may do so. This requires that you supply the 
starting and ending addresses of the five tables described in 
the section on special features and set a byte called MANUAL 
to some non-zero value. This MANUAL byte is located at $0003 
and is currently equal to zero. The assembler tests this byte 
and if zero, performs automatic table setup. If non-zero, the 
assembler picks up the table start and end addresses from the

 following locations: 
SOURCE BUFFER BEGIN $0004 
SOURCE BUFFER END $0006 
MACRO NAME TABLE BEGIN $0008 
MACRO NAME TABLE END $000A 
MACRO ACTIVATION BUFFER BEGIN $000C 
MACRO ACTIVATION BUFFER END $000E 
MACRO TEXT BUFFER BEGIN $0010 
MACRO TEXT BUFFER END $0012 
SYMBOL TABLE BEGIN $0014 
SYMBOL TABLE END $0016 
NOTES:

 1) The Macro Name Table and the Symbol Table must be an even 
multiple of 8 bytes in size!

 2) The assembler uses a large stack area to maintain all its 
temporary variables and buffers. This stack requires 0720 hex 
bytes of RAM starting at FLEX’s MEMEND and growing down from 
there. This implies two things: if manually setting up the 
tables you must leave this space free and if you want to move 
where the stack resides, you must set MEMEND accordingly as 
the assembler will always place its stack so that it sets up 
against MEMEND.

 3) When manually setting up the tables, you will probably want 
to use all the space between the end of the assembler itself 
and (MEMEND-$0720). Thus the lowest table would start just 
after the last byte of the assembler as found on the disk and 
the highest table would end at (MEMEND-$721). 

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