Sega multigame- Works!

A bit of progress to report. The Multigame hardware came up last night
fully functional with the menu system. :-)

***********Techy part:************

It was a bit more complicated than I thought. :-/ The main problem was
that it turned out I couldn't use 0xf000-0xffff in ROM without hardware
modification. (0xd000-0xdfff, 0xe000-0xefff, and 0xf000-0xffff all decode
 from the same location in the PROM on the CPU board, so it's tricky to get
0xf000 to map to something *on* the CPU board since the backplane bus
transceiver is active.)

The menu system now resides at 0xc000-0xc7ff, that's right below RAM, and I
can control it without messing with anything else in the PROM. I store the
graphics for the menu in the Space Fury bank of memory. When the menu is
called it switches to bank 2, reads the graphics into vector RAM, and then
jumps to 0xc000 area to run the menu. Works dandy. :-)

There's a couple little things left to do-- I've got the current 22V10
based GAL design crunched down to a 16V8, but it needs to be tested. Once
that's done I can design the PCB and do a run of boards.

*********End Techy Part***********

The upgrade is pretty "clean" right now-- A daughtercard, a little PCB
that plugs in where the Security Chip goes, and a replacement PROM.
Everything is socketed, no permanent modifications to the CPU board
required. The actual hardware should work for raster games too. (Need a
different menu/eprom obviously.)

With a little luck the whole thing might be available around December?

-Clay

Actually, if you want to write your own game, you could do it with the
Daughtercard and have about 768K of usable bank-switched ROM at your
disposal. ;-)

Clayton N. Cowgill Engineering Manager
_______________________________________________________________________
/\ Diamond Multimedia Systems, Inc. clay@supra.com
\/ Communications Division http://www.supra.com/
Received on Tue Nov 4 09:40:39 1997