Re: PAL Checksums

[Fred Townsend]

Declan Moriarty wrote: > I'm in a mess (What's new?). I need to find the checksums on four > PALs, 3 x PALCE 22V10 and 1 PAL18V8 > > /history > > Trouble in a machine of mine (Industrial PC, isa bus) has been traced > to a PAL. The manufacturer sent a set of 4, and the thing wouldn't > boot at all :-(. Pull one and put back the old, and I can boot. So > they sent another 4, with exactly the same results :-(. The latter > four have checksums. There is some issue in the machine about sets of > PALs, but they obviously have things wrong. > > The same problem with both sets makes me think they could all be > wrong. The machine is too elderly to freight over to them, and I need > to check my set of PALs against their checksums. ` > > /end history > > This country seems to have nothing to do this in the hands of anyone > I know or can leverage for a favour. My eprom programmer is a PB10 > (The old isa bus job) in a very old pc kept for the purpose, and an > old old old picstart plus. > > I'll build something if I have to. What do you suggest? > I suggest you quit messing around with check sums and get to work. ;-) Who was it that offered the defination of insanity as repeating the same experiement and expecting different results? Your boolean equations, and therefore your check sums, must be right or couldn't get it to boot with one of the old PALs. Ordinarly PAL programmers automaticly checksum so if there was a problem I think the programmer would say so. Your symtoms suggest you are running ripple logic with faster PALs.  If so, you are trying to fix a bad design rather than a simple compoent failure. In short a hard road to hoe. Here is where I'd start. Check your power supply. Make sure it is absolutly clean. Faster devices are more sucesptable to noise. Add bypass caps if you don't see them on the PALS. Check out the power supply electrolytics. See if you can find low power equivalents for your PALs. Quarter power versions are ideal. That does not mean switch to CMOS. The idea of using low power bipolar versions is they are much slower devices. It's not to save power. Remember speed kills. Fred Townsend