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as68 - 68000 Assembler, version 1.01
(c) copyright 1982 Steve Passe all rights reserved
Table of Contents
Chapter 1 Introduction 1
Chapter 2 Usage 5
Chapter 3 Pseudo-ops 9
Chapter 4 Mnemonics 12
Chapter 5 Expressions 15
Chapter 6 S File Format 17
Chapter 7 Error Messages 19
Chapter 8 Differences 23
as68 Manual Introduction
Chapter 1
Introduction
The as68 assembler is a disk to disk assembler for the
Motorola 68000 micrprocessor chip. Written in the c
programming language, it may be used as a cross assembler on
any machine supporting c, or as a native assembler if
compiled with a c that produces 68000 output. It's
directives and mnemonic set closely follow that of the
Motorola Resident Structured Assembler.
Source Program
The input to the assembler is an ascii text file,
consisting of a series of statements written in the assembly
language. Each statement consists of one or more fields
within a line.
The assembler is free format within each line, i.e. there
is no need to start a specific field of a statement in a
particular column. Fields are separated from one another
with whitespace (tabs or spaces).
Statements
There are 3 basic statement types. The most common is an
assembly language instruction or mnemonic. It is a command
to the assembler to produce a machine operation code to
carry out a specific action. The second type of statement
is called an assembly directive or pseudo-op. Pseudo-ops
tell the assembler how to assemble the program. The third
statement type is called a comment. It is ignored by the
assembler, it's purpose being to allow the programmer to
insert descriptions of what the code is doing within the
text of the source program. Comments may exist as the final
field of the other two statement types.
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as68 Manual Introduction
Instruction Statements
An instruction statement consists of from one to four
fields:
[label] <mnemonic> [operand] [comment]
Label Field
The first field, the label field, is optional. It is used
to create a symbolic name for the address of the code
generated by the following assembler mnemonic. This label
is stored in the symbol table and any references to it
evaluate to the associated address. The label field may be
the only field of a statement and multiple, label only
fields may follow one another. In all cases the label(s)
will evaluate to the address of the first mnemonic to be
assembled after the label(s) is specified.
Labels are composed of alphanumeric characters and may be
up to 30 characters long. All characters of a label are
significant, as is the case of alphabetic characters (i.e.
"Foo" is different than "foo"). The first character of a
label must be either alphabetic or the character '.'
(period). Following characters may also include the
underscore (_), dollarsign ($), and the digits '0' thru '9'.
Labels starting in any other than the first column must be
terminated with a colon (:). Certain symbols are reserved
for the use of the assembler and thus may not be used as
labels. These include "SP", "USP", "SR", "CCR", "A0"
through "A7" and "D0" through "D7".
Mnemonic Field
The second field is the mnemonic or assembly instruction
field. It will always be present in a statement except in
the case of a label only statement (label only statements
might more properly be described as assembler directives).
If the line is unlabeled the mnemonic field must be
preceeded by whitespace.
A mnemonic will consist of from 3 to 5 ascii characters,
the case of which is not significant. This assembler
recognizes the standard Motorola instruction set. The
-2-
as68 Manual Introduction
complete mnemonic instruction set is described in chapter 4,
"Mnemonics". Many 68000 instructions may work on different
data sizes. The desired data size is specified by appending
a length modifier or data size code to the mnemonic. A '.b'
extension specifies a data size of byte (8 bits) while '.l'
will cause the data size to be a long word (32 bits). No
extension will cause the data size to be a word (16 bits).
A '.w' extension may be used for data sizes of word,
although this size is the default and as such the '.w'
modifier is unnecessary.
Operand Field
The operand field is necessary only for those statements
whose mnemonic requires an operand(s). It will contain one
or two operands. When two operands are present they must be
separated with a comma (no whitespace allowed between
operands). The first of two operands is refered to as the
source operand while the second is the destination operand.
Comment Field
The comment field is optional and consists of all text
following the above fields.
Directives
Label Field
Labels used with directive statements follow the general
rules of those used in assembly statements with one
important exception: they may only be used with the
following directives:
1. EQU
2. SET
3. DC
4. DS
5. MACRO (unimplimented in ver. 1.xx)
Directive Field
The directive field contains an instruction to the
assembler as to how the program should be assembled. This
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as68 Manual Introduction
includes such things as the base address of the program,
setting of symbol values, allocation of program memory
storage, conditional assembly, etc. The complete list of
available assembly directions is given in chapter 3,
"Pseudo-ops".
Operand Field
The operand field of a directive statement will consist of
zero or more operands, as needed by the pseudo-op in
question. Multiple operands are separated with a comma (,).
No whitespace may exist between operands.
Comment Field
The comment field is identical to that used in instruction
statements and is optional.
Comments
Comments may exist alone as separate statements. In such
cases an asterisk, (*), must be the first character on the
line.
-4-
as68 Manual Usage
Chapter 2
Usage
Cp/m
The command line format is:
as68 [sourcedisk:]<sourcefile>[.ext] [option[ option]]
where:
sourcedisk is the optional disk specifier for the source
program file. If not given the source disk
defaults to the logged in disk.
sourcefile is the source file name. It must meet all
cp/m requirements for a legal file name.
ext is an optional cp/m file extension
identifier. By default the assembler expects
source files to have an ext of ".sa".
option is one of several possible options in
assembly. Whitespace must separate multiple
options when they occur. Individual options
are described below.
Options
The following options are available:
-5-
as68 Manual Usage
- e, destination of error messages. If absent all error
messages will go to the console by default. If
present, one or more of the following destinations may
be specified:
* c, error messages to the console.
* e, error messages to a file named
"sourcefile.err". A disk specifier may follow the
'e' option extension. Otherwise the default disk
is the source file disk. For example, 'eec:'
would send error messages to the file
"c:sourcefile.err".
* f, errors reported in listing.
* l, error messages to the cp/m list device.
- l, destination of assembly listing. If absent no
listing is made. One or more of the following option
extensions are available:
* c, listing to console.
* f, listing to a cp/m file. The file will be named
"sourcefile.ls" and will reside on the same disk
as the source file unless overridden by a
following disk identifier. For example, to place
the listing on both the console and the b disk,
use 'lcfb:'.
* l, listing to cp/m list device.
- o, type and destination of object file. If not present
the object file will be in Motorola 'S' FILE format and
will be placed on the same disk as the source file.
* s, object to a cp/m file. The file will be named
"sourcefile.mx", the output file will be in
Motorola's 'S' FILE format. A disk designator may
follow the 's' option (i.e. 'osd:'), specifing
that the output file should go to other than the
sourcefile disk (in the above example it would go
to drive d).
* x, no object file to be made.
s, set the symbol table size. The symbol table
requires 8 bytes plus the length of the symbol for each
-6-
as68 Manual Usage
entry. The argument should be in decimal bytes. The
symbol table defaults to 2000 bytes (decimal). To
reserve 3500 bytes the option would be: 's3500'.
- t, truncate source code lines in listing. This option
will cause the source code lines sent to any open list
channel to be truncated at the normal wrap position
(see option 'w' below). It defaults to being off, a
't' in the command line will turn it on.
- w, set the value of wrap. Source code lines in the
listing(s) will normally be 'wrapped' to the next line
if they extend beyond the column number specified by
this option. If the 't' option is active this option
specifies the column beyond which source lines are
truncated. The default value of 'w' is 80, but can be
set between 60 and any reasonable number of columns.
Note that this number should be set to the width of
your list device, it is not the number of columns of
source code to a line (i.e. a value of 80 allows 40
characters of source per line after accounting for the
40 columns used by the line/loc/code fields).
Examples
- as68 foo lf ecf<cr> would assemble foo.sa and create:
* foo.ls, the listing file.
* foo.err, the error file (as well as send error
messages to the console and the listing file).
* foo.ro, the s file object (by default).
This would be the normal assembly invocation.
- as68 bar ox ecfb:<cr> would assemble bar.sa and create:
* b:bar.err, the error file on drive b: (and send
error messages to console).
No object or list would be created. This method would be
used during assemblies that one knows will generate
some errors. Since the source comes from a: and only
one file is created, on b:, the disk access time is
minimized and sufficient information is placed in the
-7-
as68 Manual Usage
error file to allow correction of the source. The
error file will be much smaller than a list file with
errors and thus will be quicker to write during
assembly and easier to scan during correction of
source.
Other Systems
The code presently supports only the cp/m operating
system. Some work would have to be done in the command line
parser to bring it up on other operating systems.
-8-
as68 Manual Pseudo-ops
Chapter 3
Pseudo-ops
Assembly Control
The following assembler directives are used to control the
assembly:
ORG is used to specify the absolute memory origin
of the code to be assembled. The operand is
an expression that evaluates to an address
within the first 64 kilobytes of memory space
(0 thru $FFFF). Any memory references outside
this range will cause an assembly error. Be
aware that the 68000 chip sign extends
absolute short addresses. Thus address
references above 32k ($8000) will access
hardware memory in the range of $FF8000 thru
$FFFFFF. This pseudo-op will cause the
assembler to generate code using absolute
short addressing.
ORG.L is also used to specify the absolute memory
origin. However, in this case the entire
address range of the 68000 is usable (0 thru
$FFFFFF). The assembler will generate code
using absolute long addressing.
RORG causes the assembler to generate program
counter relative code. The memory range
restrictions of the "ORG" directive apply.
RORG.L causes the assembler to generate program
counter relative code as above, however the
expression in the operand field may evaluate
to any value within the 68000's address
-9-
as68 Manual Pseudo-ops
range.
END signals the end of the assembly language
program.
Symbol Definition
The following directives control the definition of
symbols:
EQU defines a symbol and sets it's value to that
of the operand. This symbol value is
permanent, i.e. it cannot be changed later
in a program. The operand may be a complex
expression but cannot make forward
references.
SET defines or redefines a symbol and sets it's
value to that of the operand. The value is
temporary and may be reset with another 'SET'
directive. Again, forward references are not
allowed.
Memory Allocation
These directives are used to reserve and/or initialize
memory:
DC fills memory locations with constant
value(s). An extension of '.B' causes
individual bytes to be filled with the value
of the operand(s). An extension of '.L' will
cause the operands to be evaluated as 32 bit
values, which are placed in 4 byte blocks,
one for each operand. No extension or '.W'
signifies that the operand(s) are to be
evaluated as 16 bit values, each being stored
in consecutive 2 byte locations. Word and
long word values are aligned on even address
boundries. DC.B directives causing the
location counter to end on an odd address
will pad 1 byte with a zero value unless the
-10-
as68 Manual Pseudo-ops
next source statement is another DC.B.
DS reserves memory locations. Again, a data
size extension may be appended to 'DS' to
specify either byte or long word allocation.
The operand specifies the number of data
cells to reserve, i.e. if the extension was
'.L' and the operand evaluated to 5, forty (5
* 4 bytes for a long word) bytes would be
reserved. Word alignment is not automatic as
in the dc directive. To force alignment
after a DS.B statement use a "ds 0"
statement.
List Controls
These directives are used to control the listing output:
LIST causes listing output (if enabled from the
command line) to be sent to each of the open
list channels. LIST is active by default and
remains so until a NOLIST pseudo is
encountered.
NOLIST causes listing output to be turned off until
a LIST pseudo is encountered.
Macro Commands
Macro commands are not implimented in version 1.xx of this
assembler.
-11-
as68 Manual Mnemonics
Chapter 4
Mnemonics
The mnemonics used by this assembler follow the standard
mnemonic instruction set as defined by Motorola. Mnemonics
may exist in either upper or lower case in the source file,
the assembler makes no distinctions.
ABCD add binary coded decimal
ADD add binary
ADDQ add quick binary, operand in range of 1 thru
8
ADDX add binary with extend
AND logical and
ASL arithmetic shift left
ASR arithmetic shift right
Bcc branch conditionally
BCHG bit test and change
BCLR bit test and clear
BRA branch unconditional
BSET bit test and set
BSR branch to subroutine
BTST bit test
CHK check register against boundaries
-12-
as68 Manual Mnemonics
CLR clear operand
CMP compare
CMPM compare memory
DBcc test condition, decrement and branch
DIVS signed divide
DIVU unsigned divide
EOR exclusive or
EXG exchange registers
EXT sign extend
JMP jump to address
JSR jump to subroutine
LEA load effective address
LINK link and allocate
LSL logical shift left
LSR logical shift right
MOVE move
MOVEM move multiple registers
MOVEP move peripheral data
MOVEQ move quick, operand in range og -128 thru 127
MULS signed multiply
MULU unsigned multiply
NBCD negate binary coded decimal
NEG negate
NEGX negate with extend
NOP no operation
-13-
as68 Manual Mnemonics
NOT bitwise compliment
OR logical or
PEA push effective address
RESET reset external devices
ROL rotate left
ROR rotate right
ROXL rotate left with extend
ROXR rotate right with extend
RTE return from exception
RTR return and restore condition codes
RTS return from subroutine
SBCD subtract binary coded decimal
Scc set conditional
STOP stop
SUB subtract binary
SUBQ subtract quick binary, operand in range of 1
thru 8
SUBX subtract binary with extend
SWAP swap register halves
TAS test and set operand
TRAP trap
TRAPV trap on overflow
TST test an operand
UNLK unlink
-14-
as68 Manual Expressions
Chapter 5
Expressions
Expressions
Expressions consist of one or more symbols combined by
binary and/or unary (algebraic) operators. Possible symbols
include:
- Symbols defined with the EQU and SET directives.
- Program labels.
- Numeric values.
- The asterisk, ('*'), which equates to the present value
of the program location counter.
Algebraic Operators include:
- arithmetic operators:
* multiplication: '*'
* division: '/'
* addition: '+'
* subtraction: '-'
logical operators:
* logical (bitwise) AND: '&'
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as68 Manual Expressions
* logical (bitwise) OR: '!'
* left shift: '<<'
* right shift: '>>'
unary operators:
* unary minus: '-'
* location counter value: '*'
Symbols
Symbols are composed of alphanumeric characters and may be
up to 30 characters long. All characters of a label are
significant, as is the case of alphabetic characters (i.e.
"Foo" is different than "foo"). The first character of a
label must be either alphabetic or the character '.'
(period). Following characters may also include the
underscore (_), dollarsign ($), and the digits '0' thru '9'.
Numbers may be represented as either decimal, hexadecimal,
or binary:
- decimal numbers are represented by the normal ascii
digits '0' thru '9'.
- hexadecimal numbers start with a dollar sign ('$')
followed by the ascii digits '0' thru '9' and the ascii
characters 'A' thru 'F'.
- binary numbers start with a percent sign ('%') followed
by the ascii digits '0' and '1'.
-16-
as68 Manual S File Format
Chapter 6
S File Format
A Motorola "S file" is similar in structure to an Intel
hex file. It consists of a series of ascii records, each in
the following format:
- The record start character, an uppercase ascii 'S',
followed by an ascii numeral, '0' thru '9':
-
* a '0' for the file header record.
* a '1' for records with short (16 bit) addresses.
* a '2' for records with medium (24 bit) addresses.
* a '3' for records with long (32 bit) addresses.
* ......
* a '9' for the tail record.
- The third and forth bytes forming an ascii hex
representation of the number of bytes in the body of
the record:
* an address field consisting of 4, 6, or 8 ascii
bytes representing the load address of the record
(record types S1, S2, S3, respectively).
- The body of the record consists of up to 16 bytes of
data, each byte represented as 2 ascii hex bytes.
- A checksum byte, again represented by two ascii
characters:
-17-
as68 Manual S File Format
-
* The checksum for each record (except the last, S9)
is the least significant byte of the 1's
compliment of the sum of the byte values of the
count, address, and data fields. (ie, everything
in the record except 'Sx').
* The checksum on the 'S9' record is
undefined/non-existant.
-18-
as68 Manual Error Messages
Chapter 7
Error Messages
- 1: statement parsing error. The occurrance of this
error indicates that the line totally confuses the
parser and no further diagnostic comments (legitimate
comments anyway) can be made.
- 2: bad character in mnemonic-psdo field. An illegal
character exists in the word present in the mnenonic
field, see chapter 1, introduction, instruction
statements.
- 3: instruction or pseudo not found in tables. Unless
error 2 is also generated the instr/pseudo word is
properly formed (i.e. no illegal characters are in it)
but not a recognized instruction.
- 4: bad character in macro field. Version 1.xx does not
recognize macros!
- 5: macro not found in macro table(s). Again, macros
are not yet recognized.
- 6: improper use of label. Most often this error flags
the use of a label on a pseudo op line that does not
allow the use of labels. See chapter 1, introduction,
directives:label field.
- 7: can't evaluate operand. The assembler cannot
evaluate the value of an operand. This may be caused
by a variety of reasons such as imbedded spaces,
unrecognized operators, unbalanced parenthesis, etc.
Additional errors will usually be reported that will
help clarify the problem.
- 8: can't evaluate equ operand. As above, generated in
the case of an EQU statement.
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as68 Manual Error Messages
- 9: can't evaluate set operand. As above, generated in
the case of an SET statement.
- 10: attempt to redefine a permanent symbol. The symbol
was previously defined via an EQU statement and thus
cannot be changed.
- 11: symbol table full. This is a fatal error and will
cause the assembly to abort. You may try again setting
an optional symbol table size from the command line.
See chapter 2, usage, options:s.
- 12: unrecognized operand. A legal operand cannot be
formed from the data in the operand field.
- 13: symbol not defined in symbol table. The symbol was
not encountered in the program up to this point.
Remember that forward references are not allowed in EQU
and SET pseudo statements.
- 14: label out of range for current addressing mode.
The value of the label is outside the limits of the
current statement. This usually is an attempt to
reference an address beyond the 32k bytes range imposed
in the short addressing mode. See chapter 3,
pseudo-ops, assembly control.
- 15: operand 1 is not valid for instruction type. The
first operand encountered is not a valid operand for
this particular instruction/addressing mode.
- 16: operand 2 is not valid for instruction type. The
second operand encountered is not a valid operand for
this particular instruction/addressing mode.
- 17: operand 1 is not correctly formed. This may be
caused by illegal use of operators, undefined labels,
etc. The assembler may or may not attempt to evaluate
the second operand. If it does you are not assured
that it will do so correctly. For more on this see
error #18.
- 18: operand 2 is not correctly formed. This may be for
any of the reasons stated above for error 17. Remember
that it could be incorrectly evaluated if error 17 was
also generated and that the second operand may be
incorrectly formed but not reported as such after error
17 occurs. This is dependant on the assembler
correctly determining where the poorly formed operand 1
-20-
as68 Manual Error Messages
ends and operand 2 starts.
- 19: code building function failed. The binary code
building function has failed to properly construct a
sequence of code for the statement. Thie error will
usually be followed with additional error #s
pinpointing the problem.
- 20: 3 bit immediate data value out of bounds, i.e. it
is greater than 7 or less than 0.
- 21: 8 bit bit field specifier out of range.
- 22: 32 bit bit field specifier out of range.
- 23: attempt to generate a bit field specifier failed.
- 24: count operand out of range (1-8).
- 25: destination register specifier illegal or out of
range.
- 26: source or destination register specifier illegal or
out of range.
- 27: attempt to generat register mask list from operand
failed.
- 28: operand failed to evaluate to a proper source or
destination effective address.
- 29: illegal destination effective address, probably
label or label with index reference.
- 30: illegal destination effective address.
- 31: illegal multiple destination effective address,
either label, label with index, or address register
indirect with predecrement or postincrement.
- 32: illegal jump effective address, usually address
register indirect with predecrement or postincrement.
- 33: 4 bit vector out of range.
- 34: expected address displacement failed to evaluate
correctly.
- 35: 8 bit displacement out of range (-128 thru 127)
-21-
as68 Manual Error Messages
- 36: 16 bit displacement out of range (-32768 thru
32766)
- 37: extent word of operand failed to evaluate
correctly.
- 38: 8 bit operand out of range (-128 thru 255, sign is
responsibility of programmer).
- 39: 8 bit extension word value out of range (-128 thru
255).
- 40: 16 bit extension word out of range (-32768 thru
65535).
- 41: 32 bit extension word value out of range
(overflow).
- 42: attempt to generate a 16 bit displacement failed,
probably out of range.
- 43: attempt to generate an 8 bit displacemnt failed,
check range.
-22-
as68 Manual Differences
Chapter 8
Differences
This list must be considered incomplete and will be added
to as the facts are brought to my attention.
In General
- As68 allows addresses assembled under an rorg.l or
org.l condition to be coerced into a short address by
enclosing the entire expression in a set of parenthesis
followed by '.s'. This allows references to the
first/last 32k with a code sequence that is 2 bytes
shorter than the long address mode. As an example:
org.l $8000
outport equ $ffa000 * port mapped into last
* page of address space
move.b d0,outport * will generate 6 bytes of
* code, while
move.b d0,(outport).s * will only generate 4 bytes
* of code
Motorola Resident Structured Assembler
- Motorola allows forward short branch instructions to
default to either long or short addressing. as68
always uses long or short addressing, forward or
backward, dependant on the presence of the '.s'
modifier on the mnemonic. Motorola will determine the
-23-
as68 Manual Differences
necessary value (short or long) automatically on
backward references.
- The value shown in listings for the DS pseudo-op will
reflect the number of bytes reserved in the Motorola
listing while the as68 listing will report the number
of elements reserved. For example the line: ds.w 2
will have a value of 0002 in the as68 listing while the
Motorola listing will report a value of 0004
Digital Research Assembler
- Pseudo-ops are required to start with a period (.) by
the Digital assembler while as68 follows the Motorola
conventions.
- Digital expects a default source file extention of ".s"
where as68 expects ".sa"
-24-
as68 Manual Differences
-25-
Index
! 15
& 15
* 16
.b extension 3, 10
.l extension 3, 10
.w extension 3, 10
<< 16
>> 16
absolute long addressing 9
absolute short addressing 9
AND 15
arithmetic operators 15
assembly control 9
assembly options 5
binary 16
comment 3, 4, 4
cp/m 5
data size code 3
datasize code 10
DC 3, 10
decimal 16
destination operand 3
Digital Research Assembler 24
directive 3, 3
DS 3, 11
END 10
EQU 3, 10
expression 15
hexadecimal 16
instruction 2
label 2, 3, 15
left shift 16
LIST 11
list controls 11
location counter 15, 16
logical operators 15
MACRO 3, 11
macro commands 11
memory allocation 10
mnemonic 2
mnemonics 12
Motorola 'S' FILE 6
Motorola Resident Structured Assembler 23
NOLIST 11
numbers 15, 16
operand 3, 4
operators 15
OR 15
ORG 9
ORG.L 9
program counter relative 9
right shift 16
RORG 9
RORG.L 9
S file 17
SET 3, 10
source operand 3
source program 1
statement 1
symbol 15, 16
symbol definition 10
unary minus 16
unary operators 16
EQU 3, 10
