68008 co-processor board complete working design available ...

[Jim Gilbert <brokerjim@gmail.com>]

Back in 1985-1987 I implemented a 68008 wirewrapped co-processor board
that ran on both my Apple II+ and my Apple IIGs.  (I never tested in
on a IIe.)

This design was based on a Motorola design note and featured some
considerable extensions:

8 Mhz 68008
128 K DRAM (Intel 64x4 FPM DRAMs)
2732 EPROM
Communication with Apple II back plane via a dedicated read port and a
dedicated write port, each attached to a Mostek 4501
256 x 8 FIFO.  These FIFOs enabled both processors to speak to the
other with relative impunity since they handled timing issues well.
68901 MFP chip serving as interrupt controller, parallel ports, serial
port (complete with full modem control), and timers for 68008.
Hardwired reset pushbutton on top edge of card.
Software:
(1)  PROM Monitor on 68008 initialized everything, maintained software
refresh of DRAM, and implemented bidirectional communications protocol
with host 6502 (read/write a byte/word/long/block, run code beginning
at x, reset).
(2) Applesoft debugging monitor on 6502 which helped load and debug
code on the 68k
(3) RAM Disk software used to test 68008 where the co-processor was
just used as RAM drive for the 6502
(4) Print spooler for the 68008 using its memory to spool for the 6502
(not sure I still have this)

I have a working wirewrapped board, block diagrams, schematics, wire
lists, theory of operation, construction and debugging guides, timing
diagrams, the works...

I built this out of parts that were mainly free samples from Motorola,
Intel, Mostek etc. back when I worked for a system company.

I used to actually sell the kit on Usenet but unfortunately the key
single component that became unavailable was Hollywood Hardware's
wonderful full-length Apple II prototyping board which I used.  To run
the card in an Apple II GS I had to use a bus extender because the GS
case is a little shorter front to back than the IIe or II+ ones
were.

I am seriously thinking of scanning and loading all this stuff into a
web site and making it public domain if anyone is interested.
As far as I can tell the 68008 and the 68901 and the 4501s are still
all available.  The rest of it is all 74 series TTL except for one 555
timer chip.

My design, was heavily influenced and inspired by the Motorola design
note but is clearly significantly different and original.

The main problem with building another one or more would be finding a
viable Apple II prototyping board that is big enough.

The 68008 software is assembly language in the AT&T syntax that was
accepted by the BSD UNIX system at work and the public domain 68K
assembler for CP/M I used on my Z/80 coprocessor (Softcard, then
Applicard).  Yes, the 68008 co-existed with the Z/80 cards...

I no longer have an Apple II.  In order to build or play with one of
these a bus extender is very valuable because you'll wear out your
backplane slot with too many insertions and extractions otherwise...

Jim Gilbert
brokerjim@gmail.com