RE: Testing Cinematronics CPU's

>So - the first thing I wanted to do was create a ROM image filled with
>nops to make the signatures readable.

[technical steps deleted]

>Someone also suggested earlier that I could hardwire the nops into the
>board. I'd like to know how this is done. I'm assuming I could tie
>certain pins to ground - thus loading all zeros through the data lines?

Yes, you can do this. All you would have to do is hard wire the "0x5f"
onto the CCPU instruction bus and it would appear that the "ROM" was
reading 5f regardless of the address being accessed. The easiest place
to do this is at location U14, where you have access to the input to the
instruction register (T13) and data register (S13).

Unfortunately, this is where the good news ends. Just to give some back-
ground, the wired NOP is generally used to perform signature analysis (SA)
on combinatorial logic (i.e. address decoding) and on ROMs. The design
of the CCPU is such that it has almost no address decoding to perform
SA on. Additionally, in today's day and age, it's much more efficient to test
the ROMs by reading them and doing a compare with a reference image.
SA was used to test ROMs way back when most people's benches weren't
equipped with EPROM programmers, plus it was a more attractive alternative
to having to have one of every ROM to swap in sequentially. All you will really
be able to test with a NOP on a CCPU is the instruction register, the PC,
a small part of the instruction decoder and some glue.

The bottom line is I don't think it will buy you very much.
If SA could have been done on the CCPU without the exorciser, I suspect
they wouldn't have bothered to make it.

For my own two cents, I think the best way to fix the CCPU is:
1) Get a new one (this is my first choice and I've fixed several)
2) Use an original exorciser or a copy (and it's documentation)
3) To quote my Bally/Midway service manual "Take two aspirin and..."

I know that replacement CCPUs are a finite resource, but then
again, so is crude oil; there's enough to last for the foreseeable future.

Sorry, I wish I had better news for you.

-Mark

Anyway - I just thought one or two of you guys might give some advice.

Thanks...

Matt

Received on Tue Jan 19 00:05:25 1999