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Question: Dump the BIOS of Amstrad XTs (PC1512/PC1640) using TL866 II Plus

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First post, by jewesta

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Hey everyone!

I have a few Amstrad PC 1512 / 1640 motherboards and always wanted to dump the BIOS directly from the chips. I know that I can use DEBUG for that and I've already managed to do so. But I want to try and read the images off the chips.

Simple question: Is it possible to do this with my el cheapo TL866 II Plus EEPROM reader? And if so, which type of ROM is compatible / do I have to select? I have tried a few without success ("bad pins", although perfectly OK when in the system) and am reluctant to just do trial and error.

According to the technical documentation here (1512) and here (1640) it should be 8k BIOS chips (Hi / Lo configuration), so a total of 16k. The Amstrads also have a third chip, the character ROM. All three chips are in a DIP 28 package.

I can see no helpful info on the chips, only Amstrad part numbers. There is no info on the back of the chips either.

Thanks!

Jens

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  • IMG_9266.jpeg
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    IMG_9266.jpeg
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    1.7 MiB
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    710 views
    File comment
    BIOS ROMs (Hi / Lo)
    File license
    Public domain
  • IMG_9265.jpeg
    Filename
    IMG_9265.jpeg
    File size
    1.79 MiB
    Views
    710 views
    File comment
    Character ROM
    File license
    Public domain

Reply 1 of 5, by weedeewee

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Most other computers of that era tend to use something similar to a 27c512, 27c256, or smaller.

Since you mention 8K, a 27C64. disable chip id

Which chips have you already tried to select in tl866 software?

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Reply 2 of 5, by mogwaay

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See if you can find the schematic for the Amstrad and check the pinot looks compatible with one of the 27xxx series ROM datasheet. I just dumped the Acorn Electron ROM last night using my TL866 and I just picked the AM27256 after matching the pinot to a datasheet. Worked great. Also interestingly the Acorn Electron ROM is not fully accessible from the Electron itself so there is a nice 'hidden' thank you message stored on it at the inaccessible locations, which is nice!

Reply 3 of 5, by jewesta

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Thank you for your input so far!

I feel a bit stupid now... AT28C64B gave me a pin detect error on pin 27. I was reluctant to "force" reading so I never tried that before posting. Based on what you guys wrote I went ahead with it and it read the ROM successfully. I compared both dumps with what I got from splitting up what I got from DEBUG and the hashes match. So that solves this mystery.

Still do not understand the pin detect error, though! Attached the schematics just fyi. I know they also are on the net.

Thanks again!

Jens

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Reply 5 of 5, by jewesta

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Hey

Today I tried to dump the Paradise EGA ROM of a 1640 (dubbed “40100” by Amstrad). To my surprise it was a 27(!)256. So on the PC1640 there are actually 2864s and 27256s on the same board. Like with the 2864s the ROM reader reported loads of “bad” pins but read the ROM fine when forced.

Just thought I’d add that here for future reference.

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