I bought another batch of 28C256's because my present ones are getting kinda tired. They sent me a tube of chinesium 28C256's rather then the atmels that I had recieved before.

They program and verify fine but they dont work in the ECM. Itll read them for a short period but then lock up and be forced to restart. Or, even worse, lock up before the cop sets and just rambles on and on randomy turning on all the outputs, while the car is running, of couse .

The checksum verifies ok, but the computer still locks when it tries to run. The memory speed is 250ns. Is this too slow? To me it seems that the min time between sucessive reads should be ~800ns with a C3 ecm. Am I missing something? Is it just cheap memory thats the problem?

 

Try burning them with higher voltage. I've had to do this a couple times.

 

The program voltage is locked at +5 volts. The atmels work fine but these dont seem to cut it.

 

I didn't think the 28c256's worked in the ecms. Any reason you're not using the 29c256 flash parts? are the 28's cheaper?

 

The 28C256's worked quite well for me. Got zillions of burns out of the two atmels I bought. One for the car, one for the test bench. I figured Id pick up a couple more of them. They work good in the burner as well. Bang it in to the burner and click 'program' and it programs it. The chips still work just that the pins are all corroded and mangled from use and abuse.

I really wish they didnt send me some junk no-name chips. Its still sort of perplexing as to why these present ones didnt work. Seems like even junk should work for a little while.

 

Is there any reason for the 28C256 not working?

 

well, the pinouts are different, A14 and something else is swapped, i forget what..a programming voltage? or something. in any case, it probably isn't a big deal cause a14 in both cases might be held in the same state hi or low in the ecm, so it would work. but maybe there is somethin slightly different with the chips, and now the different pin-out is biting you. I have seen some chips that have funny reaction to voltages. I had some 27c256 otp proms one time that would program fine, but the data looked like garbage out, and when we bumped the vcc up a bit, they looked better, I'm talking like 4.8 volts to like 5.1 volts, so not much.

i also checked mouser for both 28c256 and 29c256, and they were around $4.50, plus or minus a few cents each, so not much price difference. both atmel.

 

I actually use them because Im romless. So the pinouts of the 28C256 adn teh 29C256 are different?

 

yep, 28c256 does have two pins different, one being a14. could explain why it starts to work, then goes flaky.

another intersting thing, apparently, a 27sf256 is also a drop in for the 27c256, although that might be obsolete.

 

All this talk of eprom pinouts is blowing some of the dust out of the back of my mind. I beleive that there was a reason that I used the 28C256 for my romless C3. Ill have to look at the pinouts to see why.