More EEPROM Experiments

When in doubt, knock them out! I took one of the read-in EEPROM images and knocked out a few bytes here and there in chosen places to see what happens to the EEPROM. Here are the results:

Installing 00 in location 04: No effect. Printer re-wrote correct value there.
Installing 00 in location C8: No effect: Printer re-wrote correct value there.
Installing 00 in location E5: Printer reports engine error on boot.
Installing 00 in location F5: Printer reports engine error on boot.

That helps eliminate some possibilities.

DC requested that I rescan, with the improved scanner, the first page that I had from a different serial number printer. Here is a swatch from the rescan:

Here’s a torrent for the image file.

Anybody in the San Diego area have an HP 2600N that I can borrow for a weekend? :-D I want your EEPROM contents!

5 Responses to “More EEPROM Experiments”

  1. Patrick says:

    B,

    I’ve determined that there are checksums embedded in the EEPROM data. The 16-bit (byte reversed) value at 0x2C-2D is a checksum for the 16-bit data from 0x00 through 0x2B. Similarly, the value at 0xAC-AD is a checksum for the data from 0x80 through 0xAB.

    I’m guessing that the printer manufacturer believes the serial number is important enough to checksum, and store twice. I have a guess where it is located — 0x22-27, and 0xA2-A7.

    I’ve got an experiment for you to try, if you have the time. Follow these steps for modifying the values in EEPROM:
    – Decrement the value at 0x24 by 1
    – Decrement the value at 0x2C by 1
    – Decrement the value at 0xA4 by 1
    – Decrement the value at 0xAC by 1
    – Power off the printer, and power back on
    – Check the serial number (print a test page, or can you check it through the printer menu?)

    Hopefully, this procedure will change the serial number. I’m looking forward to hearing how it goes!

    – Patrick

  2. Patrick says:

    Clarification — the checksum is calculated by summing up each of the 8-bit values. I got carried away with typing “16-bit”…

    Patrick

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