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JohnBHanson · 14th Sep 2017, 9:02 am

Yes the first byte is being corrupted to 0ffh sometimes.
Two options

1. There is a buffer between the eeprom and the data input to the 6802 that is not being enabled fast enough after reset the the cs or oe input to the rom is not going
active. If you can add these signals to the logic analyser trace.

2. There is something else on the bus that is pulling all the address lines high.
(Try removing all the other uv-eproms and see if you get a better reset trace).

I think 1 is more likely.

What is happening is the first byte read by the processor is getting changed to 0xff. Thus the processor is reading the wrong vector and then starts executing the program from the wrong location.

With eraseable eeproms you can get the effect that the program deteriorates over the years but is still readable at slow speed. If you are sure you can read the uv-eeproms successfully then try re-programming them without erasing them. Just to be sure are the labels still stuck on them as a few years of normal light will start to erase uv-eeproms.

Just an idea.

14th Sep 2017, 9:02 am	#16
JohnBHanson Heptode Join Date: Aug 2009 Location: Worthing, Sussex, UK. Posts: 661	Re: Help with 6802 Microcontroller Yes the first byte is being corrupted to 0ffh sometimes. Two options 1. There is a buffer between the eeprom and the data input to the 6802 that is not being enabled fast enough after reset the the cs or oe input to the rom is not going active. If you can add these signals to the logic analyser trace. 2. There is something else on the bus that is pulling all the address lines high. (Try removing all the other uv-eproms and see if you get a better reset trace). I think 1 is more likely. What is happening is the first byte read by the processor is getting changed to 0xff. Thus the processor is reading the wrong vector and then starts executing the program from the wrong location. With eraseable eeproms you can get the effect that the program deteriorates over the years but is still readable at slow speed. If you are sure you can read the uv-eeproms successfully then try re-programming them without erasing them. Just to be sure are the labels still stuck on them as a few years of normal light will start to erase uv-eeproms. Just an idea.