Re: somebody tell me what went wrong.

[Peter Gargano <peter@ntserver.techedge.com.au>]

Craig Marcho wrote:
> 
> ... dig out a 40-pin IDE hard drive ribbon cable and some 90 degree  and
> straight headers...

How long is this IDE cable? 18 inches?

> ..I come inside and
> plug the socket into my PB-10 and read the eprom into buffer. It doesn't
> match the bin that I programmed into the eprom in the ZIF socket. I notice
> also that everytime I read the device into buffer, the checksum is different
> each time...

Assuming you have not inadvertantly swapped any pins (and you claim to have
checked this) then it sounds like you may have a noisy bus problem. I would 
not have even attempted to run an ECM from an EPROM located on the end of an
18" bus. You may have better luck with an EPROM emulator, as the DATA bus
lines would be better buffered, but even running an emulator with a long data 
path to the ECU is also a source of noise pickup.

Years ago, I designed an add-on board for a popular Z80 microcomputer. It
worked fine as a prototype with point-to-pont wires (to the 40 odd chips),
and quite a long data and address bus. Lots of people liked it and asked if 
I could make a kit with a real PCB. After a lot of PCB laying out with black 
tape (what, no Protel?), and a prototype that worked fine. I had 50 PCBs
made up and started selling them. It didn't take too long for people to
realise that the maximum bus length for their unit to be reliable was in
the order of 3 inches. This situation was not to everyone's liking, despite
my prototype still happily running with an 18" bus. Anyway, to cut a long story 
short, I've been personally burned by noisy busses, and I first suspect long 
cables will be problem area.

My suggestion is to shorten the cable to the absolute minimum, and see if
you still have a problem.

Peter.
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