Multigame update!

Hi all!

After some helpful discussions with Dave and Al on a problem I was having I
now have the first cut of the Multigame daughtercard running on my G-80
system at home. It plays Zektor and Space Fury. Hitting the NMI (test)
switch drops into a menu system. ;-)

Anyway, it's coming along nicely. I learned some interesting things along
the way:

The PROM on the CPU board controls a 74ls245 bus tranciever. (No
problem...) However, even though the EPROM board has its own tri-state
control, the CPU PROM does the *same* thing. Cost me a few days on *that*
one.

The other trick is the PROM itself. It decodes A15,A14,A13,A12,A11,A10 but
with A13 and A12 OR'd (I think, I don't recall now) together. This makes
for a "strange" memory-map of block access. (I include the mapping at the
end of this text.)

What happens is that some chunks of memory can be resolved in 2K pieces,
other sections result in 6K chunks. What this basically means is that I
can't allow accesses to the Universal Sound Board RAM (0xd000) and the
Vector RAM (0xe000) (on the backplane bus) and allow access to peripherals
and Menu-system (0xf000) on the CPU board with the memory decoder
as-implemented on the CPU board.

No big deal, since my board has it's own memory decoding system, but until
I found out that the "helpful" little PROM was fighting with me it was a
real bugger to get working. :-) Special thanks to Dave for insisting the
problem was in the PROM, which was right...

I'll put up a screen shot of the menu system titlepage this afternoon
(hopefully)...

-Clay

G-80 Address PROM decoder
address= 0000-03FF prom location= 0000
address= 0400-07FF prom location= 0001
address= 0800-0BFF prom location= 0002
address= 0C00-0FFF prom location= 0003
address= 1000-13FF prom location= 0010
address= 1400-17FF prom location= 0011
address= 1800-1BFF prom location= 0012
address= 1C00-1FFF prom location= 0013
address= 2000-23FF prom location= 0010
address= 2400-27FF prom location= 0011
address= 2800-2BFF prom location= 0012
address= 2C00-2FFF prom location= 0013
address= 3000-33FF prom location= 0010
address= 3400-37FF prom location= 0011
address= 3800-3BFF prom location= 0012
address= 3C00-3FFF prom location= 0013
address= 4000-43FF prom location= 0004
address= 4400-47FF prom location= 0005
address= 4800-4BFF prom location= 0006
address= 4C00-4FFF prom location= 0007
address= 5000-53FF prom location= 0014
address= 5400-57FF prom location= 0015
address= 5800-5BFF prom location= 0016
address= 5C00-5FFF prom location= 0017
address= 6000-63FF prom location= 0014
address= 6400-67FF prom location= 0015
address= 6800-6BFF prom location= 0016
address= 6C00-6FFF prom location= 0017
address= 7000-73FF prom location= 0014
address= 7400-77FF prom location= 0015
address= 7800-7BFF prom location= 0016
address= 7C00-7FFF prom location= 0017
address= 8000-83FF prom location= 0008
address= 8400-87FF prom location= 0009
address= 8800-8BFF prom location= 000a
address= 8C00-8FFF prom location= 000b
address= 9000-93FF prom location= 0018
address= 9400-97FF prom location= 0019
address= 9800-9BFF prom location= 001a
address= 9C00-9FFF prom location= 001b
address= A000-A3FF prom location= 0018
address= A400-A7FF prom location= 0019
address= A800-ABFF prom location= 001a
address= AC00-AFFF prom location= 001b
address= B000-B3FF prom location= 0018
address= B400-B7FF prom location= 0019
address= B800-BBFF prom location= 001a
address= BC00-BFFF prom location= 001b
address= C000-C3FF prom location= 000c
address= C400-C7FF prom location= 000d
address= C800-CBFF prom location= 000e
address= CC00-CFFF prom location= 000f
address= D000-D3FF prom location= 001c
address= D400-D7FF prom location= 001d
address= D800-DBFF prom location= 001e
address= DC00-DFFF prom location= 001f
address= E000-E3FF prom location= 001c
address= E400-E7FF prom location= 001d
address= E800-EBFF prom location= 001e
address= EC00-EFFF prom location= 001f
address= F000-F3FF prom location= 001c
address= F400-F7FF prom location= 001d
address= F800-FBFF prom location= 001e
address= FC00-FFFF prom location= 001f

Clayton N. Cowgill Engineering Manager
_______________________________________________________________________
/\ Diamond Multimedia Systems, Inc. clay@supra.com
\/ Communications Division http://www.supra.com/
Received on Mon Jun 2 10:36:42 1997