HP 9872T Trouble Shooting

[vassilisprevelakis]

(03-01-2023 01:28 PM)cruff Wrote:  By the way, the 9872C schematics seemed to show a discrepancy with the mapping of some of the address bus bits to the ROM address pins. I'm not sure if this is real or not, as it also showed the ROM enable signal (labeled as "F1") going to an address pin on the 36000 ROM instead of the CE pin.

Yes they got the pins mixed up in the schematic. The connections are correct in the 7220C schematics. On the actual device the connections are (of course) correct, or it wouldn't work even with a functioning ROM :-)

Nevertheless, on the 9872C they got the screen labels wrong for the +5V and Common test pins, next to U28. They are actually reversed which caused some early testing confusion on my part as I was unlucky to use these test points for my initial connectivity testing.

As an aside, although the 9872C and then 7220C were identically priced, the RS232 model had additional functionality (ability to generate arcs and circles) plus more ROM and expandable RAM.

Finally, the 7221C which uses a compressed version of graphics language instead of HP-GL, can be turned into an 7220C by simply replacing the 2 8K ROMS with those of the 7220C.

If anybody wants the ROM dumps of the 7220C, I have uploaded them to the series80 website.

These are ASCII files with lines starting with the hex address followed by 32 bytes of data encoded as 2-digit hex numbers.

I have also uploaded the combined file with lines starting with the address in hex followed by 16 words of data each encoded as 4 digit hex numbers.

U55: https://www.series80.org/Misc/7220C-U55-MSB.hex
U56: https://www.series80.org/Misc/7220C-U56-LSB.hex
And the combined MSB and LSB ROMs is at:
https://www.series80.org/Misc/7220C-COMBINED.hex


Vassilis
http://www.series80.org