Cinematronics BPROM alternatives

I dunno about anyone else, but I'm rather sick of problems related to
sourcing and programming the old bipolar PROM chips on game boards. Tons of
games use BPROMs but they can be very hard to source, they can be expensive,
and finding an old programmer box that supports them is even tougher. I
used to have an older programmer that could handle 82Sxxx parts but that's
it. I tried burning 6301, 74Sxxx, and such equivalents but they failed. My
present programmer, a Xeltek SuperPro/Z cost me only $100 and it can program
all sorts of EPROMs, flash SPLD, flash EEPROM, PAL, GAL, and stuff like
that.

I repair several Cine CCPU boards each year for people and the dam BPROMs
are always what I fear the most will have to be replaced. Since there are
five 74S288 (32 x 8) type BPROMs on the CCPU, I decided to start with that.
I chose an Atmel SPLD that is really cheap ($1.50), available from almost
any electronics distributor, is available in a small SOIC package, and is
supported by my programmer (and almost every programmer on the market
today). I wrote separate programs for all five BPROMs (located at E8, C14,
D14, E14, J14) using Atmel WinCUPL which is free. It produced the JEDEC
(*.jed) files needed to program the chips. The new chips are flash or
EE-SPLD. They are as fast as the original BPROMs. I made a chip adapter
socket today and tried the new chip in all five locations on a known good
CCPU board and they all worked fine. I have designed a tiny new PCB that
will convert the new chip pin-order to plug directly into the CCPU original
locations.

I have also designed a replacement for the larger BPROM (74S287 256 x 4)
located at F14. For a first effort, it is based on a Xilinx XC9536. I
couldn't get all of the data to fit into a cheaper SPLD but I'm open to
suggestions if someone has a smaller cheaper chip in mind for the job. I
still have to build a socket adapter to try it. For now, the design is done
and the code is written in VHDL but I haven't tried it in a running board
yet.

Also, I don't care much for old windowed EPROMs either. They're okay and
they've proven their worth, and some guys out there still sell NOS parts at
good prices but it's not like you can just buy them anywhere you want to
anymore. For the Cine CCPU (or Vectorbeam Space War), I decided to try
something else just for fun. I know someone will say "seen it, old news"
but just in case someone else might find it interesting I'm going to say it
anyway. I purchased some new readily available flash parallel EEPROM chips
that my programmer supports. The OnSemi CAT28C16A is a 2k x 8 flash memory
with the same pinout as a standard UV 2716 except that on the new chip, pin
21 is "/WE" and not "Vpp". If the CCPU had wired pin 21 as tied high, the
new chip would just plug in and work. As it is, pin 21 is tied low and so
that would hold the new chip in "write" mode and we don't want that. The
solution I used tonight just to try it out was to program the chip, bend the
pin outward just a little and plug the chip into the socket with pin 21
hanging out over the side. The board ran fine.

The advantages of the EEPROM are:
-more widely available than UV 2716 chips
-cost is very low
-no UV needed to erase it, programmer does it instantly
-has 100 year retention
-has no window so it can't be corrupted by external light sources
-can be instantly reprogrammed for other games

There's no 4k x 8 equivalent to the 2732 chip that I am aware of, at least
not in current distributor stocks. If there was, you could do this same
type of replacement for games such as Armor Attack and Solar Quest.
However, there is a 64k x 8 device that is in a 28-pin package. The cool
thing about it is that it can be plugged into the original socket with 4
pins at one end hanging out and it has everything needed except power. One
tiny wire jumper fixes it. Or, you can install 28-pin sockets into the
original 24pin sockets and add the jumper to that. Also, there's a couple
of extra address pins to tie down but that's super simple. You can even
program up to 8 games into the new chips and add switches to operate the
extra address pins to create a multi-game CCPU. That doesn't address the
obvious control panel wiring differences or the audio issues, but still.
You can make a general CCPU that can be used on the bench to test several
different games at the flip of a DIP switch or two. This has been done
before and is in fact old news but to my knowledge the chips suggested were
older UV parts. I'm suggesting to use the newer flash CAT28C64 type as a
superior replacement device. Designing a CPLD to reroute the control panel
lines would also be easy but I like Zonn's more practical approach of
redefining the input lines within the game source code such that all the
inputs for all the games match and then you could build a universal control
panel.

Working with the SPLD and CPLD parts to replace old custom logic gets me a
little pumped to dive in and start collecting whole sections into CPLDs.
There's been lots of talk about possible single-chip CCPU boards emerging in
the near future and that would be exciting. I'm very new to such devices so
I expect that a project that big is beyond me for the moment, but I can see
how more experienced designers can really get into this stuff and pull it
off. I might not be able to make a single-chip clone board on my first try,
but I bet I could get it under 15, maybe 10.

My plan presently is to get a couple hundred of the little 32x8 BPROM
converter PCB's made so if anyone is interested in them, let me know. I may
work something out for the 256x8 some time soon after that.

William Boucher

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Received on Thu Oct 1 23:56:35 2009