If we help him do what he wants, maybe WE will learn something too.

He doesn't want to buy other chips. He wants to make THESE chips work. There's no reason why he shouldn't do that, is there? It's his hobby project. It's his budget. It's his kitchen.

It's not WRONG for him to change chips, but it's not WRONG for him to decline to do so. Frankly, I don't think he can make this work for a number of reasons, but none of the reasons involve the EEPROM or the MCU. The reason it will be difficult to make it work is that he's not considered timing constraints, and that he's operating his MCU outside specified limits, and that he's trying to make a PCB for the first time, and that he's got no test equipment by means of which he can determine what's wrong when the circuit doesn't behave as he expects. I suspect he also hasn't yet heard of metastability.

What I personally believe is that he should first see to it that his MCU circuit works. Then he should, with that MCU circuit, ensure that he can program the EEPROM from the MCU. If, having reached a point at which he can program and verify his MCU, he wants to insert his circuit to force the MCU to execute instructions fed to it from his parallel port, he should go ahead and attempt that. It IS his project, after all.

If he's followed this forum for any length of time, he knows that a large percentage of the "problems" that have been discussed involve IAP and ISP. I don't blame him for wondering whether that's worth pursuing. He probably is aware of the reset/FLASH-corruption issues that pop up from time to time.

He has on hand an MCU that's essentially an 80C31. He has an EEPROM which, among other things, he wants to program in-circuit. He's never said whether he has the means to program the EEPROM on its own, perhaps to see whether his MCU circuit works. I'd guess he doesn't, else he'd not be trying to build an EEPROM programmer. If I were going to advise him, I'd tell him to delay the EEPROM programming effort, and start by programming an SRAM from the PC's parallel port. He can always get a BBRAM and plug it into the SRAM socket once he's written his code to it. He can then migrate to an EEPROM, if that's what he wants to do.

The key is that he wants to do it himself, and in his way. If he wanted to buy a solution, he'd have done that already. Goodness knows, those DIY-at-home PCB kits cost more than a decent kit of premade PC board and parts for an MCU circuit.

What's more, if those FLASH-based IAP/ISP-capable parts were all they're advertised to be, we'd never be discussing reset circuit problems, or IAP/ISP problems. Let's try to help him do what HE wants, rather than what WE want.

RE