Electronics > Repair

HP 3478A: How to read/write cal SRAM

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m k:
Data lengths
8, 5, 8, 6, 6, 14, 2, 11, 3, 10, 4, 9, 5, 4

so

8,
5, 8,
6, 6,
14,
2, 11,
3, 10,
4, 9,
5,
4

Last is unknown, but others are ok, one empty.
First is only 8 long starting from 0x20.

fenugrec:

--- Quote from: radar_macgyver on March 21, 2024, 04:17:52 am ---I have a 3478A prototype version (at least, I think it's a 3478A, it has no label or serial number).

--- End quote ---

Interesting... if you have a ROM dump and want to investigate, you're looking for this function :

https://github.com/fenugrec/hp3478a_utils/blob/master/ROM_disasm/dc118.d48#L285

may end up somewhere else but will be similar (a short loop with movx to read the RAM, bitwise 'and' with 0x0F, add every field, then check)

radar_macgyver:
@pqpass, thank you for decoding my hex dump.

U502 is a 24-pin ceramic DIP with no window, and no stickers on it. I guess it must be prototype firmware. I don't have an EPROM reader so I can't do a dump. Maybe I should get one...

When comparing against my 6500, here's what I get:

TestDMM6500HP 3478Notes30 mV29.7 mV29.7 mVWas very noisy0.3V0.30030.3003Was very noisy3V3.00283.003030V30.029030.029870V70.038570.040The max my PSU could do100mA100.000124.241.0A1.00051.244100k99.987299.980Using DMMcheck10k10.0023610.0014Using DMMcheck1k0.09996260.99955Using DMMcheck100100.1650100.155Using DMMcheck5VDC4.999855.0000Using DMMcheck5VAC4.999184.9998Using DMMcheck
I used my bench power supply for the DC voltage tests except the last two, those are from a DMMcheck. The resistance tests are also from the DMMcheck. Looks like the amps ranges are clearly not calibrated, though the DC volts and ohms show very good results. This leads me to think, combined with the fact that the dump reads back the same '0x49' for all offsets < 0x20 that it may be due to the GPIB interface I'm using (0x20 = 32 = first printable char).

m k:

--- Quote from: radar_macgyver on March 22, 2024, 04:41:36 am ---combined with the fact that the dump reads back the same '0x49' for all offsets < 0x20 that it may be due to the GPIB interface I'm using (0x20 = 32 = first printable char).

--- End quote ---

If so then all after 0x7E can be the same, excluded for what ever reason.

You can concentrate to address 0x1F and few before that.
Those missing from first set should be 0x40.

There are two possibilities.
Either the first set is really 8 long, or those first 0 values are missing.

pqass:

--- Quote from: radar_macgyver on March 22, 2024, 04:41:36 am ---@pqpass, thank you for decoding my hex dump.

U502 is a 24-pin ceramic DIP with no window, and no stickers on it. I guess it must be prototype firmware. I don't have an EPROM reader so I can't do a dump. Maybe I should get one...

When comparing against my 6500, here's what I get:

...snip...

I used my bench power supply for the DC voltage tests except the last two, those are from a DMMcheck. The resistance tests are also from the DMMcheck. Looks like the amps ranges are clearly not calibrated, though the DC volts and ohms show very good results. This leads me to think, combined with the fact that the dump reads back the same '0x49' for all offsets < 0x20 that it may be due to the GPIB interface I'm using (0x20 = 32 = first printable char).

--- End quote ---

There may be some funny business going on with values at addresses <0x20 and >=0x80.   
Have you seen this (reply #134) version of a python script that corrects for some default string conversions that may be occurring.   Please re-run.

Otherwise, the meter tracks pretty close to the DMM6500 (except for the amps ranges).

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