Re: 13 sector or 16 sector Disk ][ card?

[dempson@actrix.gen.nz (David Empson)]

Perry Dueck <pdueck@pli.mb.ca> wrote:

> Perhaps a bit of a stupid question, but here it goes anyways (for my
> benefit if nothing else):    :)
> 
> How would one distinguish between a Disk ][ card which is capable of 13
> sectors (original...wayyyyy back in the early days of the Apple ][), and a
> 16 sector Disk ][ interface card?  Are the ROM chips marked with a special
> number to distinguish between the two different kinds or something?

The only difference between the original 13-sector card and the later
16-sector version are two chips.  They are labelled "PROM P5" and "PROM
P6" on the card legend (white writing).

I've never seen a 13-sector card (at least, not close enough to note the
chip numbers), but the PROMs are labelled as follows on the 16-sector
card:

PROM P5: 341-0027
PROM P6: 341-0028-A

PROM P5 is the 256 byte boot firmware that appears in memory at $C600
(assuming the card is in slot 6).  PROM P6 is the "logic state
sequencer" which is the main part of the state machine that implements
the low-level byte access routines.  It is not directly addressable by
the CPU and doesn't contain what you would normally consider to be
"machine code".

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand