Your Commodore - Commodore Is Awesome

1 C 6 4 PROGRAMMING
MACRO
ASSEMBLER
Be the master of your
machine code program
with this extensive 3
pass macro assembler
By I. Goffe
have been available for the
M Commodore 64 since the
arrival a of the machine, but sadly many
such n pieces of software are scarce in
the y shop today. I have noticed a steady
revival a of assemblers, thanks largely
to s magazine such as this, it is especially
true of the 6510+ assembler in the
May/June
s
issue of its sister magazine
Commodore e Disk User, which offers
many m more facilities than its commercial
b counterparts. My Macro assembler
l is intended to be yet another
valuable
e
tool to the machine code
programmer, with the added bonus of
r
macro, and conditional assembly; this
allows
p
much more structure to be
implemented a into your own machine
code c programs.
k Presented here is a sophisticated 3pass
a 6502/6510 Macro Assembler that
supports g many advanced features,
including:
e
Full
s
macro assembly with parameter
passing;
Linkable source files;
Including directly from disk;
Symbol table/ buffer space memory
configure;
Conditional assembly (IF, THEN,
ELSE);
Symbol table cross-referencing;
Selective assembly output;
Full DOS support;
Extendable capabilities.
The assembler can be configured
to work with either disk, or cassette
filing.
The Assembler - Getting
Started
The assembler code runs from S6E00-
SA000. To initialise the assembler from
a cold start type: SYS 28160, this redirects
the RESTORE key to allow
you to enter the assembler command
mode with a single stroke key press.
If you should change the RESTORE
key vector use SYS 28160, which will
re-initialise once more, The use of a
cold start also clears the current
symbol, macro directory, and macro
library areas.
Once a cold start has been issued
as above, the program title will be
displayed, at this point as Basic wedge
was to be used to enter the assembler
command mode, but I wanted the
system to be able to run alongside an
extended Basic if there are no memory
conflicts. I opted for the idea of being
able to call up the main assembler
command mode by pressing a single
key which emulate the Basic command
'SYS 28215' which calls up the
assembler command mode via a warm
start.
To summarise, pressing RES-
TORE whilst in the basic editor will
automatically do the Basic command
'S YS 28215' to jump into the assembler
via a warm start.
Extra Note on Compatability
with Action Replay
Some ROM routines which are called
inside the assembler seem to corrupt
Nv he n the assembler is first run, to get
around this problem follows these
steps...
11. Type SYS 64738 to jump into a
normal reset
2. Press the reset button on the back
of the cartridge to exit back to the
'FASTLOAD' interpreter which will
allow the assembler to operate. In this
case all FASTLOAD/ Warp loading
can be used in conjunction with the
assembler, making source file 110
extremely fast and effective,
The RESTORE key does not work
correctly with TASILOAD' installed,
so a manual 'SYS 28125' needed to
be typed to jump into the assembler
command mode.
Entering Source Files
The source files are maintained in the
standard Basic editor, so you will not
need the assembler present for actually
entering the source. As in Basic only
lines 0-63999 are valid.
The source must follow a set
format, however, true field-tabulation
is not required for LABEL, OPCODE,
OPERAND but some form of correct
syntax needs to be followed. In general
the syntax would be one of:
LABEL OPCODE OPERAND;
LABEL
OPCODE;
OPCODE OPERAND,
Note that if a label is not followed
by an opcode then a comment (1) is
expected. A comment can be used in
any available field. A space is needed
in between the 'fields', and where
applicable quotes must be set out in
the text correctly,
eg):
10 LDA 1 0 ! space between LDA
and 10
20 LABEL ! a comment is needed if
no following opcode
30 DINCLUDE "name" ! opening and
closing quotes needed,
Thirty Two Y O U R COMMODORE