For Sale: HP-71B MultiMod ROM Emulator

[mfleming]

(12-24-2022 09:48 AM)nickyvarian Wrote:  

(03-20-2021 04:35 PM)Dave Britten Wrote:  Got my MultiMod today, and it seems to be working well, according to VER$.

I ran into an issue flashing a ROM image, and the terminal output went haywire, frozen on a "Commit?" prompt a couple seconds into uploading. I had to remove the power jumper to get the module responding again. But now the ROM table is corrupt - it's showing HARD on ROMs 1-5, which shouldn't be possible, and I can't figure out how to unset this. Is there some way to clear/reset the ROM table so I can start fresh? The MCLR jumper didn't appear to do it.

I am also facing the same problem as you.

I really should have posted the fix I sent Dave so others who encounter the problem can also fix their MultiMod. You must make sure of two things; You are sending the hex file image of a ROM (found in the github subdirectory DAT) and not the actual ROM binary, and you have the Xon/Xoff protocol set for flow control.

The error occurs when you fail to set Xon/Xoff flow control and the resulting data buffer overflow causes junk to be written to the ROM table held in RAM. No problem unless another condition occurs in the hex file you are uploading - the letter 'C' followed by a carriage return. The 'C' character is interpreted as the COMMIT command and the default action when a carriage return is hit is to write the new corrupt ROM table content in RAM back to flash. That error was fixed in the code after Dave reported it.

There are two ways to fix the problem. The first is to re-flash the PIC processor itself with an updated emulator and ROM image. You'll find MMimage0104.hex (emulator) and MULTIMOD0104.hex (emulator + default ROMs) in the HEX directory. You can use a PIC programmer or Appendix A shows you how to use the Windows boot loader client. Don't have a PIC3 or PIC4 programmer (or don't know what I'm talking about)? No problem.

The second way to fix the problem is to download the file repair.dat from the HEX directory. Connect the serial cable after turning off the 71B (the PIC goes to sleep after two minutes, giving you time to hook things up). Get into the monitor (XON/XOFF SET!) and type the following commands

"E" "0" for erase chip 0
"I" "0" to flash the repair.dat file that you upload

After you've finished uploading the file, type the undocumented command "X" and confirm with "Y". The flash image of the default ROM table will be updated to its original state and the PIC will reboot. The RAM copy of the table will be restored.

~Mark

[vaklaff]

Mark, big "thank-you" from a new happy user. My 71B just ran its first Forth commands and looked comfortable.

For the record, it took 12 days from Mark to me in Czechia, including the delay caused the customs.