| Products > Test Equipment |
| HP8656B fractional-n microprocessor |
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| Tomorokoshi:
Regarding Artek: https://www.eevblog.com/forum/testgear/artek-manuals-digital-download-orders-working-again/ |
| ekoloski:
Excellent note about Artek! It's wonderful that they're continuing on and making these manuals available. In case anyone is interested, I've posted the files on github: https://github.com/ekoloski/hp8656b Posted here are a short writeup on the process to dump the original ROM, the kicad files for my replacement board, the original disassembled code from the HP Mask ROM, and my modernized replacement for the 32U4. I hope that this could help someone else in the future who may need to perform a similar recovery on another mask ROM. |
| Tony_G:
This is outstanding Ed - Congrats on the work. Have you tried it in the 8656B yet? How'd it go? Look forward to hearing from you, TonyG |
| ekoloski:
Thank you! It does work well in my spare 8656B. While writing the 32U4 firmware I spent quite a bit of time verifying that the timing of the new version matches up with the original. The 1820-2004 Fractional-N controller seems to be as sparsely documented as the 1820-3618 mask ROM. I couldn't find a datasheet and was sort of flying blind on any timing constraints. An arduino was used to simulate serial commands, so I could send whatever I wanted and vary the timing between commands. The new 32U4 and my only functional mask ROM were wired up in a breadboard with a logic analyzer on their outputs and everything was compared, then delays were added to compensate. I was also able to verify the various test modes and mostly validate signature analysis. I don't have a proper signature analyzer to check with, but the waveforms all matched up. Once that was all done I threw it into the 8656B to confirm. |
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