Apple ][ notes

*^B *FEB0G *E000G	Enter Integer BASIC “Cold” launch; erases any loaded program
*^C *FEB3G *E003G	Enter Integer BASIC “Warm” launch (continue); preserves program state
*3D0G	Enter Integer BASIC via DOS call vector (requires DOS to be loaded)

Brilliantly, the Apple ][ ROM comes with a complete listing, which is invaluable for looking up constants like these. The relevant section looks like this:

FEB0: 4C 00 E0  XBASIC   JMP   BASIC      TO BASIC WITH SCRATCH
FEB3: 4C 03 E0  BASCONT  JMP   BASIC2     CONTINUE BASIC

And indeed if you disassemble that part of the Monitor, you get:

*FEB0L

FEB0-   4C 00 E0    JMP   $E000
FEB3-   4C 03 E0    JMP   $E003

There are three useful entry points for returning to the Monitor:

hex    dec
$FF59  -167  ENTER MONITOR RESET, TEXT mode, "COLD START" 
$FF65  -155  ENTER MONITOR, ring BELL, "WARM START" 
$FF69  -151  Go to MONITOR

The source listing labels these three RESET, MON, and MONZ, respectively. In BASIC, use the CALL statement, eg:

>CALL -151

The entry point for the mini-assembler is $F666. So to enter the mini-assembler from the Monitor:

*F666G

And from BASIC:

>CALL -2458

Of course, you can use the RESET button to return to the Monitor. Perhaps a more elegant way would be to use one of the Monitor’s entry points, eg:

!$FF69G

*n^P

where n is the desired slot number. On Virtual ][ it’s slot 6 by default, thus:

*6^P

Strangely the Redbook (p. 71 [PDF p. 76]) says that ^P:

Sets printer output to I/O slot number (X).

which seems a bit nonsensical. But it seems that the ^P command executes whatever is in $Cn00, thus one could do, eg using slot 6 ($C600):

*C600G

Or, from BASIC, eg one of:

>CALL -14848
>PR#6

These are only the most common commands:

Boot into the desired DOS version using some known working DOS boot disk. If you have a program you’d like to execute at boot, LOAD it now, eg:

>LOAD FUNIONS

Otherwise, create a dummy BASIC program so you don’t get an error at boot, eg:

>NEW
>10 END

Initialise the disk:

>INIT HELLO

(HELLO appears to be the canonical choice, though you can use whatever you like.) This saves the current program to the disk with the name HELLO, which will be executed at boot.

By default, this creates a “slave diskette” (1970s–80s terminology!) suitable for booting on machines with your current memory configuration. If you want a relocatable DOS boot disk, you’ll now want to use MASTER CREATE, eg one of:

>BRUN MASTER CREATE
]RUN MASTER

Looking at the HELLO startup file on my custom Integer-BASIC-only S-C Macro Assembler disk, you’ll see lines like:

>LIST 80,100
   80 CALL -936: PRINT "CATALOG":
       PRINT "INT"
  100 PRINT "BLOAD S-C.ASM.MACRO.1000.
      2.0": CALL 4096

There are actually invisible ^D characters there which cause those PRINT statements to effectively execute DOS commands. If you could see them, they’d look like:

>LIST 80,100
   80 CALL -936: PRINT "^DCATALOG":
       PRINT "^DINT"
  100 PRINT "^DBLOAD S-C.ASM.MACRO.1000.
      2.0": CALL 4096

It’s important that these be inside the quote marks.

 10 FOR A = 935 TO 941
 20 READ B
 30 POKE A,B
 40 NEXT A
 50 POKE 56,167
 60 POKE 57,3
 70 CALL 1002
 80 END
100 DATA 72,41,63,145,40,104,76,27,253

At first glance, this appears to write some data to $3A7 (935), then a 16-bit word $3A7 to address $38. But there’s 9 bytes of DATA – and only 7 locations (935 through 941) to put it in. So that 941 should really be 943 (or the 935 should be 933) so that all of the bytes are written.

That DATA is machine code, which looks like this when disassembled:

*3A7:48 29 3F 91 28 68 4C 1B FD

*3A7L

03A7-   48          PHA
03A8-   29 3F       AND   #$3F
03AA-   91 28       STA   ($28),Y
03AC-   68          PLA
03AD-   4C 1B FD    JMP   $FD1B

At system boot, the contents of $38 are:

*38.39

0038- 1B FD

Hey, that address looks familiar! From this it appears that address $38 is being patched to execute the above code at $3A7 before it jumps to its original location, $FD1B. This works just fine, provided that DOS isn’t loaded.

After booting DOS, the situation changes slightly. Now $38 points to a DOS I/O handler at $9E81. Not only that, there are protection routines that prevent you from changing this, eg:

*38.39

0038- 81 9E
*38:1B FD

*38.39

0038- 81 9E

This is because DOS is intercepting all I/O requests – including those from the Monitor. After much digging, I was able to locate the address in DOS, $AA55, which points to the original I/O handler ($FD1B). When DOS boots, it copies $38 (labelled KSW) to $AA55 (labelled KSWTRUE), then patches $38 to its own I/O handler at $9E81. With DOS loaded, this works:

*3A7:48 29 3F 91 28 68 4C 1B FD

*AA55:A7 3

After a RESET, $38 will be reset back to $FD1B. I’ve found it best to change $38 before reconnecting the DOS I/O hooks so that it will save $3A7 to $AA55, eg:

*38:A7 3

*3EAG

*38.39

0038- 81 9E
*AA55.AA56

AA55- A7 03

In fact, this is the same procedure that the Applesoft snippet tried to use (]CALL 1002 is *3EAG); it failed due to the DOS I/O interception protection.

>LOAD
>SAVE

Doesn’t get much easier than that, does it?

Which version? I suggest the S-C Macro Assembler 2.0, not the S-C Assembler II 4.0; despite having a higher version number, it’s four years older!

$1000 or $D000? $1000. On the original Apple ][ with the Programmer’s Aid routines, $D000 is already used for the high-resolution graphics system.

The documentation helpfully suggests:

You will probably wish to move the version of the assembler you
usually use, with your favorite driver and EXEC loader, to your
working disks. Do it!

The overall procedure looks like:

1. Create a new bootable DOS disk using the INIT / MASTER CREATE commands (see Formatting disks above).
2. Copy the desired assembler version, eg S-C.ASM.MACRO.1000.2.0, to that new disk.
   This could be done with the COPY (Integer BASIC) or COPYA (Applesoft BASIC) programs, or an external utility like Copy II Plus.
3. Edit the HELLO BASIC program to execute the assembler upon boot. At minimum, it would need to include a line like:

   10 PRINT "^DBLOAD S-C.ASM.MACRO.1000.2.0"
   20 CALL 4096

   Note that the ^D character is invisible.

S-C Macro Assembler 2.0 supports three different 80-column cards:

1. Apple ][ “Redbook” Reference Manual (January 1978) – 30th Anniversary Edition
2. Apple ][ BASIC Programming Manual
3. Programmer’s Aid #1: Installation and Operating Manual
4. [Apple] DOS Quick Reference Card
5. Beneath Apple DOS

Feel free to contact me with any questions, comments, or feedback.