 
How To Create A Customized Apple DOS 3.1 Master Disk Image
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1. Customize the appdos31.asm file as you wish. You may need to change
   the syntax to suit the assembler that you choose to use. Pay close
   attention to the overall size of the binary generated, and to page
   boundaries as per the warnings throughout the comments in the source.

2. Assemble the source to produce a binary. Rename the binary to RAWDOS.
   You may need to include the file attributes in the name depending on
   the utility you use to add the binary to a disk image.
   
3. Open a DOS 3.1 master disk image in a disk image manipulation utility,
   and then copy the newly assembled binary to the image, replacing the
   existing original RAWDOS binary.
   
4. Boot the image in an Apple II emulator. Many emulators do not support
   booting a 13 sector per track image directly, but that isn't a problem
   (see Note 1 below for more detail):
   
	a. Boot a DOS 3.3 master disk image that contains the Apple's
	   BOOT13 binary.
	   
	b. Enter "BRUN BOOT13" and wait for the prompt to enter the
	   slot number to boot from (default=6).
	   
	c. Eject the DOS 3.3 disk and mount the DOS 3.1 image that has
	   your custom RAWDOS file on it.
	   
	d. Press enter.
	
5. Once the DOS 3.1 disk has booted, enter "RUN MASTER.CREATE" and follow
   the directions.
   
   
Note 1:

Apple's DISK II disk controller is outfitted with two 256x8 PROMs. One of
these PROM's contains the 'Phase 0' boot code that is responsible for
loading up and running the 'Phase 1' code located sector 0 of track 0 on
a DOS boot disk. The second PROM is generally referred to as the 'logic
state sequencer' PROM and is used to control disk accesses.

The initial shipments of Apple's DISK II disk controller were outfitted with
P5 (boot) and P6 (logic sequencer) PROMs. These versions of the PROMs were
specific to 13 sector per track disks, which was the format used when DOS 3.1
(and DOS 3.2) was released. With the release of DOS 3.3, the format changed
to 16 sectors per track. Apple made newer PROMs available (P5A and P6A) to
support the new disk format. While you cannot boot a 13 sector per track
disk directly with the newer P5A boot PROM (it is specific to 16 sectors
per track), the P6A logic-state sequencer has no issue reading and writing
both 13 and 16 sector per track disks.

Indeed, that is why Apple provided the BOOT13 binary (and the "BASICS"
diskette) when DOS 3.3 became available. With a controller outfitted with
the newer PROMs, it's simply a matter of booting a DOS 3.3 disk, and
entering 'BRUN BOOT13'.

   
 Scott LaBombard
 labomb@rochester.rr.com
 12/07/2013
