Help to read out Eprom code

Hello and thanks for taking the time to read my post.

I have a device I use in my business, several actually, that use a 256k (32K x 8bit) Eprom to hold what is probably a rather simple program and/or a look up table of some sort. Basically, as best as I can determine, the system will output a specific DC signal level for a very short period at the exact same moment in time over and over with different levels for different times. That's all it has to do, really.

I have no diagrams for this part of the device but the components on the small maybe 1.5" x 2" pc board are all marked. What I need to do is get access to what's inside the Eprom so I can make changes to some of these levels. I have an EMP 10 programmer and, if I get hold of an SO IC adaptor, I can read what's inside the Eprom. However, I'm not an engineer so I have no idea what I'm looking at so I'd just be poking around looking at smily faces and hearts and things.

Is there a way to go backwards from this point not knowing any more than this?

How would I need to proceed or is there someone out there who can help?

Thanks, George

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First, I would contact the original supplier-manufacturer of the device, if at all possible...

Second, failing that, it is a relatively easy to 'reverse engineer' your device.

You'll need to know what kind of processor the EPROM is being attached to. Then get the binary data from the eprom to some kind of .bin file and print that out. The EMP10 and it's software will do that,piece of cake.

Next you'll need a disassembler for that processor on the board, these are/should be available off the web.

Next spend a whack of time reading up on that processor,instruction set, and spend a lot more time trying to disassemble the eprom's data.

IF you can get it done in less than 6 months YOU're better than most so called 'software engineers'. While it's NOT damn near impossible, it can be a real 'treat' to figure out the code. The original programmer could have used so really neat tricks, the assembler/linker could do some neat stuff too.

All that being said, I made a whack of cash doing the same thing for a silly

8Kbyte program.Enough to retire at 50 and enjoy it !

Enjoy...some challenges can be fun,others a real b*tch Jay

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j.b. miller

Wow - what did you make???

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John Harlow

$10 per bit! He was real happy that I could and DID do it. I got 20K down, which paid for the 'new' PC(it was a long,long time ago) and a lot of the coffee I drank,while I figured out the 'cute' code the original programmer did.Some was for clever timing issues, others were to keep guys like me from figuring out what he did. It makes me appreciate the PICs with only 35 instructions,those can be done in my sleep!

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j.b. miller

ISTM that the art of disassembly is becoming black magic these days, partially because of the presence of bloat. Some years ago I had problems with some commercial software which the vendors had no idea how to fix (they had long since lost or unloaded the original writers, maybe even the source). After some disassembly I could generate a patch, and I even sent it to them. They were totally amazed.

Chuck F ( (
   Available for consulting/temporary embedded and systems.
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That, and the invasion of lawyers and law-makers that came up with such ill-conceived things as the DMCA, which, taken at face value, would illegalize disassembling somebody else's code without their explicit consent. That reduces the area where disassembly can be applied both legally and usefully to such a small area that the remaining field collapses to almost nothing.

Hans-Bernhard Broeker (
Even if all the snow were burnt, ashes would remain.
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Hans-Bernhard Broeker

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