(Topic ID: 206901)

Data East MPU won't load EPROM


By Opiate

1 year ago



Topic Stats

  • 31 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by CactusJack
  • Topic is favorited by 6 Pinsiders

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3 key posts have been marked in this topic

Post #22 What is the function of a CPU? Posted by CactusJack (1 year ago)

Post #26 Description of a "NOP" CPU, a tool for troubleshooting. Posted by CactusJack (1 year ago)

Post #29 More about a "NOP" CPU. Posted by CactusJack (1 year ago)


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#2 1 year ago

Well, for some you can look up the datasheet for the chip, and see if all the signals out match correctly to the inputs. But that would take ages. If you're not getting anything from Leon's, you need to go back to basics. How is your chip socket for your Eprom? Do you have your jumpers right? Is your processor running? Do you have a known good processor to replace it with for testing?

#4 1 year ago

How's your clock signal? What voltages do you have on pins 39, 37, and 5?

#7 1 year ago

Which chips did you socket?

#9 1 year ago

Wow. How's pin 40? Behaving correctly?

#11 1 year ago

Why would 4v read low with the probe? If it's like 4.5v that's normal. But the whole blanking being on and off is very strange. Something isn't making a good connection somewhere.

#13 1 year ago

Sure, it's possible. It's sure not supposed to have two data lines tied together. I don't like your logic probe, though. 4.5 is high in anybody's book.

Edit: Before you start cutting legs on your PIAs, take a look at the resistor bank, RA4. Those can short as well.

#18 1 year ago

Well, that makes me feel better about your meter, at least I want to clarify: Do pins 28 and 29 have continuity to each other? I feel like you weren't the clearest in your description there.

#20 1 year ago

That's actually fantastic news. Pins 28 and 29 being together was bad juju. Pin 2, 40, and 6 being 5v is fine. There's no program, so the data lines won't be altering high and low, they're fine. The other ones are hard to tell without a scope. When you put your data probe on them, do they pulse? Or are they steady state? I don't suppose you have anything that can check the frequency of your clock, do you?

#24 1 year ago

Well, when you had the two data lines tied together, that was data being corrupted and thus the program couldn't start. Now that's fixed, you still can't start. The question is why, and I'm not sure I can get you much farther without a scope. If you want to, you could make the assumption that clock, VMA, and E are all fine, and start checking the address buses for movement. But without a scope, or the knowledge to use one at least, you can't know if the clock, VMA, or E are fine or not.

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