Hi all, branadic, I did the same thing. But as long as it is difficult and time consuming to change RAM contents, what would you do?
Does anyone have the 2720GS connected to a working GPIB-bus?
I checked the commands, if you send a request SW, it should answer with the firmware version, here 61.
Additionally to the beforementioned commands, there are also some System / Service / Internal Calls (adress table in 9D3C / 9D6A):
comSC_9D7A
LDX #tblSC_9D6A
BRA L9D82
comIC_9D7F
LDX #L9D3C
L9D82
LDA <L005F
CLR <L005D
which I am looking at.
I hope to find commands to modify NVram contents in the device.
maxwell3e10: Thank you for your time, pages 15 to 21 of 99 would be interesting, as they are poor in the pdf.
There must be a manual with around 150 instead of 99 pages (including volume 1?), does someone have this?
I updated the valhal2.zip-file with disassembly-listing.
One thing to note: Valhalla connected the address-decoders 74138 and 74154 in an unusual way:
the outputs are not addressed in linear order, because for example A15 is wired to IC4/1 (input A), not IC4/3 (input C), as one would expect.
Update: Branadic, the oven adjustment must be -0.5V (ca. 53°C) for RV1, not -0.8V (71°C). RV2 is for overtemp, where 71°C are correct.
Attached you find a simulation. I put the zener D7 to constant 69°C to get fixed 6.3V. The AD590 generates a current in µA proportional to absolute temperature (PTAT), at 27°C 300µA, which results in 5.8V at R7+R8=19320 Ohms
I would run the reference at a lower temperature, e.g. 45°C, depending on ambient and internal device temperature.