Old 8085 Code

Thread Starter

DHembree

Joined Sep 10, 2018
9
While I have gained *some* experience in microprocessor code development over the years, I claim no expertise in it. I'm fairly certain I know the answer to this question, but I have been surprised in the past so I thought I would ask it:

I have been asked to replicate and modernize an old design that is based on the 8085 microprocessor. There is quite little documentation regarding the program flow. If at all possible, I would like to not re-invent the wheel. Is there ANY method by which I can re-use the code contained in the EPROM memory, i.e some modern processor that can emulate the 8085 so the code doesn't need to be completely re-developed. Yes, even I'm laughing at this, but I thought I would ask.

Thanks!
Dan
 

JohnInTX

Joined Jun 26, 2012
4,338
Welcome to AAC!

I don't think you'll be able to run the 8085 executable in EPROM on anything but an 8085. A quick search for 8085 emulators turned up not much. If the code was written in assembly, you could use one of the online disassemblers to get the raw source (no comments). Usually you can trace the flow and get an idea of what's happening but it's a chore.
I suppose you could write an 8085 interpreter that emulated the instruction set and registers and run that on some fast modern chip but that sounds like real work too and you still would not have a handle on the underlying code.

If you are stuck with reverse engineering the code, one of the Virtual 8085s that run on a PC may help you trace the code. You would need to generate an Intel HEX file from the EPROM contents.
http://virtual8085.blogspot.com/p/what-is-virtual-8085.html
https://www.softpedia.com/get/Programming/Other-Programming-Files/Virtual-8085.shtml

I've found that it's usually easier to just run through the operation of the device and generate a specification from that. Once you have the specs and flow, coding a new chip is relatively straightforward.

Sorry I don't have more. I did a ton of 8085 back in the day. Interesting to see it's still around.
Good luck!
 
Last edited:

John P

Joined Oct 14, 2008
1,846
What do you have to work from here? An assembly language file with comments, perhaps? If so, omeone who knows a processor's assembly language could very likely write a pretty close equivalent to it. But if it's just the hex file extracted from an EPROM, it's going to be a much harder job.
 

Thread Starter

DHembree

Joined Sep 10, 2018
9
Welcome to AAC!

I don't think you'll be able to run the 8085 executable in EPROM on anything but an 8085. A quick search for 8085 emulators turned up not much. If the code was written in assembly, you could use one of the online disassemblers to get the raw source (no comments). Usually you can trace the flow and get an idea of what's happening but it's a chore.
I suppose you could write an 8085 interpreter that emulated the instruction set and registers and run that on some fast modern chip but that sounds like real work too and you still would not have a handle on the underlying code.

If you are stuck with reverse engineering the code, one of the Virtual 8085s that run on a PC may help you trace the code. You would need to generate an Intel HEX file from the EPROM contents.
http://virtual8085.blogspot.com/p/what-is-virtual-8085.html
https://www.softpedia.com/get/Programming/Other-Programming-Files/Virtual-8085.shtml

I've found that it's usually easier to just run through the operation of the device and generate a specification from that. Once you have the specs and flow, coding a new chip is relatively straightforward.

Sorry I don't have more. I did a ton of 8085 back in the day. Interesting to see it's still around.
Good luck!
John,
Thanks for the input. I might try the disassembly route to what it yields. I have no idea how it was originally developed. The documentation I have has a general program flow chart which is better than nothing, but there are output decisions (or calculations) made in the code that are going to be more difficult to re-construct.

Thanks again!
 

Thread Starter

DHembree

Joined Sep 10, 2018
9
What do you have to work from here? An assembly language file with comments, perhaps? If so, omeone who knows a processor's assembly language could very likely write a pretty close equivalent to it. But if it's just the hex file extracted from an EPROM, it's going to be a much harder job.
John P,
Thanks for the reply. All I have are two EPROMs on a board. It's not going to be easy.

Dan
 
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