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I have used IDA to disassemble a big EPROM (27020) but there remain a large number of code sections which haven't been disassembled. Here is a typical one where I have identified the beginning and end (it was probably written in C):

            db  55h      push bp
            db  8Bh      mov bp, sp
            db 0ECh
            db 0A0h
            db  96h
            db  11h
            db 0FEh
            db 0C0h
            db 0A2h
            db  96h
            db  11h
            db  3Ch
            db    3
            db  75h
            db    5
            db 0C6h
            db    6
            db  96h
            db  11h
            db    0
            db  8Ah
            db  1Eh
            db  96h
            db  11h
            db 0B7h
            db    0
            db  8Ah
            db  87h
            db  2Fh
            db  13h
            db  5Dh     pop bp
            db 0C3h     retn

My question is, is there any easy disassembler I could feed this (or a pure hex version) into which will disassemble for me? Yes I can do it manually but there are hundreds like this so it would be really impractical and besides, this is only the first step in figuring out this code. I tried to search but after a few days figured it was time to ask those more knowledgeable than myself.

  • how did you load it into IDA and what CPU type did you use? IDA disassembles this byte sequence just fine (both in metapc and 80286 modes). – Igor Skochinsky Dec 26 '19 at 19:16
  • First I loaded the hex file but that was a mess. I am more a hardware guy so I just followed the advice of someone who apparently wasn't too sure. In any case I converted to binary and tried that and got much better results. The problem is that this is a large (27020) EPROM so there is a very large amount of code, and of course there is a lot of data mixed in along with it. This means I have to go through IDA somewhat manually to identify what is code and what seems like data. This is a very long process with this large a file. – Peter Gottlieb Dec 27 '19 at 5:38
  • As I have some specific tasks I want to perform, my initial focus is on identifying where in the code the options are set. I have 2 different versions of code which (so far as I know) only differ by options selected at startup, however, the code has a lot of areas which disagree, so either routines are different or simply rearranged on linking. Too early to tell. I have the EPROM in the device and hooked to a logic analyzer so can see the startup and have already identified many of the setup routines from basic (loading interrupt vectors) to more complex (programming the associated FPGA). – Peter Gottlieb Dec 27 '19 at 5:44
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You can open IDA, go to the beginning of the file, press shift, hold it, scroll to the end of the file - which will result that the whole code is selected, and press 'c' for analysis.

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Since you mentioned hex files, one additional issue you could have hit is difference between 16-bit and 32-bit code. Hex file loader probably defaults to 32-bit while this code seems to be 16-bit. Editing segment properties to mark it as 16-bit after loading should give you better results.

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  • Thank you Igor. Yes, the code is almost certainly 16 bit. – Peter Gottlieb Dec 27 '19 at 19:36

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