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Thread: Reading the Eprom data from a vintage UV Eprom CPU

  1. #1

    Default Reading the Eprom data from a vintage UV Eprom CPU

    Possible or not question:

    I have a 1986 vintage multi-standard video monitor whose system controller uses a vintage MC1468705G2 UV eprom. It was done this way so that all the monitor's controls could be touch buttons with memory for the various settings/selections .

    This CPU was originally programmed at the factory by transferring data from another programmed EPROM, on a small programmer board, described in the application note on the link below. The data sheet for this IC is also on the link below.

    I have a blank MC1468705G2 device which is now a rare part itself and one & only working programmed device from the original monitor. Without it the monitor is useless. I want to program the blank IC as a spare part, but the original 1986 vintage factory files (presumably BIN files) are not available.

    Is it possible to read the contents of the MC1468705G2 UV eprom from the working device to create the image, or is this not possible with UV eprom CPU's of this type ?

    http://matthieu.benoit.free.fr/cross...C1468705G2.pdf (the CPU's data sheet)

    http://matthieu.benoit.free.fr/cross...N907A_REV0.pdf (application note for programmer pcb)

  2. #2

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    Quote Originally Posted by Hugo Holden View Post
    MC1468705G2
    Depends on _IF_ the algorithm exists. I will check my Needham EPROM programmer.

    I wonder if the 68764 and/or 68766 are compatible. I have algortihms for those...

    68764 is not an MCU
    Last edited by ardent-blue; July 16th, 2017 at 07:19 PM.

  3. #3
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    My BP Microsystems device programmer claims to support the MC68HC705G4 device, but not the MC68HC705G2 device.

    I don't see it in the Data I/O device support list either.
    http://www.dataio.com/Support/Device-Search

  4. #4

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    Yes, the whole problem seems a lot more tricky when the EPROM is part of a CPU. I'll look up the MC68HC705G4 device.

    Presumably an Eprom writer can write CPU/Eproms, if they are able to program the specific device in the first place and as part of the verify process read them too. So maybe there is one out there that can do it.

  5. #5

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    It looks like the bootstrap part is programming and verifying the internal eprom from the external (ep)rom.
    So there could be a tedious way to get the contents but you need a rom emulator to do it:

    You can use the supplied circuit in the datasheet and set switch S3 to 'verify only'
    In the emulated rom you need to set all 8 kBytes (the CPU seems to supply 13 address lines??) to all 256 possible values and reset the programmer and check if 'verified' comes up, if not try next value and repeat.

    I don't know how the verify agorithm works, if it stops after the first error then the process can be much faster, or after checking all the bytes but it might be a way to get the contents.

  6. #6
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    Quote Originally Posted by Hugo Holden View Post
    Yes, the whole problem seems a lot more tricky when the EPROM is part of a CPU.
    And it supports inhibiting the ability to read what was written after programming.

  7. #7

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    In this case only the MCU itself can verify its contents against the external rom so you have to go through some hoops..

  8. #8
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    It's not at all clear to me (reading the MC1568705 datasheets) that verification can be separated from programming. The documents appear to say that the progression from programming to verification is automatic. Perhaps you could remove Vpp when RESET/ is raised so that nothing gets programmed, but that's just a guess.

  9. #9

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    Hi gertk,

    I could see how this could work. It doesn't really matter how time consuming it is. Where would I acquire a Rom emulator ?

    I would also have to modify the programming board to make 100% sure that it couldn't alter the contents of the existing chip.

    Its a real shame they didn't use a separate CPU & UVeprom.

  10. #10
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    Wait'll you get a modern MCU with security fuses....

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