COAET" • r

If you read last issue's installment, you may remember
that that article involved interfacing an Assembly language
routine to an Apple/// Pascal program. The procedure and
techniques we used were exactly the same as those used in
Apple II Pascal. Those of you out there who are familiar with
how Apple Pascal links up with Assembly language will see
that the way invokable modules are created and used
directly parallels the Apple Pascal technique. Therefore, I
would highly recommend the Apple II Pascal Operating
System Reference Manual chapter on The Assembler for
some background material on writing Business BASIC
ivokable modules.
Getting Down to Details
Alright already, enough discussion and reference. How di
I do it? Glad I asked. Well, here goes.
Assembly language routines which can be used from
Business BASIC are written with the Apple // / Pascal system.
In general, the code is created in the Editor, assembled
with (surprise!) the Assembler, saved to disk, then used
from the Basic program.
Here's a nice bonus effect of having both Pascal and
BASIC served by the same operating system and disk format:
the same Assembly language routine can often be
used by both BASIC and Pascal with little or no modification.
As a demonstration of that claim, our first BASIC
invokable module will use exactly the same Assembly language
file as was used last time with Pascal, which prepares
the system for a cold start. If you didn't enter the file last
time, have since erased it, or (shame on you!) don't have the
previous issue, I'll repeat it here, with instructions. (Back
issues of the March-April 1982 issue of Apple Orchard are
available.)
First, enter the Pascal Editor, and type in this file: (some of
the comments have been omitted this time)
.PROC RESTART
COLD_START .EQU 65
$65
BRK
parameters
;COLD_ST ART's
number is
;To signal a SOS
call
;Tells which call
.BYTE COLD_START
.WORD PARAM_TABLE ;Points to the
PARAM_TABLE .BYTE 00
para ms
.END
;see Mar-Apr Apple
Orchard for details
;COLD_START
has no
Then, leave the Editor and save the file by typing
"QW.D2/RESTART', substituting a different disk drive
name for .D2 if you wish. Then press "A" to assemble the
file. Answer ".D2/RESTART" to the "Assemble what text?"
question, using something other than .D2 if you didn't save
to Drive 2 from the Editor. When asked "To what code file?",
answer by typing a dollar sign. This will cause the output file
to be called RESTART.CODE on the same disk as the
source file. Press [RETURN! when asked for an output file
name.
Once the assembly has been finished, you should have a
real, live, bona fide invokable module!. To prove it, boot your
Business BASOC 1.1 diskette, then put the diskette with
RESTART.CODE on it in the built-in disk drive. Type
"INVOKE .DI/RESTART.CODE" to load the module from
disk Then type "PERFORM REST ART' and watch the fun.
Your screen should say "INSERT SYSTEM DISKETTE
AND REBOOT' in 40-column text mode. You've just written
and executed an invokable module! That wansn't so
bad, was it?
Now that you've got the basics of writing invokable
modules, you should be able to handle the whole story,
which appears in (ta-daa!) Apple's new technical note,
Apple / / / Business BASIC and its Assembly Language
Interface. This note should be available from the IAC soon,
or write to the author (that's me) in care of Apple Orchard
for more information on writing invokables or unlocking
any of the other Apple / / / mysteries.
For further information: be sure and read (and reread)
your Standard Device Drivers Manual. It's got great gobs of
goodies in there, and it will likely answer some of your
favorite technical questions about the Apple //I- Also, the
Apple / / / Pascal manuals are worht a perusal or two.
And now, folks, it time to practice your invocations!
May -June 1982 67