Read and restore calibration constants from a HP 34401A

[e61_phil]

Hi,

As shown here in the forum, for many meters some (undocumented) functions exists to read the calibration data via GPIB.

Does anyone know, if such commands exists for the 34401A? I can't find anything until now.

Best regards
Philipp

[meandeev]

Hi,
I did it on the hardware way with a test-clip on the eeprom (see the picture), but you have the unit switched on and the processor in "endless" reset, so that its pins are in a high impedance state.

I used different test clips at the processor seen in the picture, that are connected with a 1k resistor.
Then I used a GQ-4X programmer (choose 93C66B-Device with  16bit NOT 8bit).

So you can read and write the eeprom.

I´m also keen on: Is there a different way to read the constants (via HPIB or serial)?

best regards
Ronny

 

[JohnPi]

There are apparently PEEK and POKE commands that might be able to read memory -- however I have never seen any documentation beyond this - https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1000001267:epsg:faq&nid=-31895.536880933.02&id=1000001267:epsg:faq which shows how to enable a 10 mA AC range.

[Hydron]

A quick update to this topic - with the help of some other forum members and other old threads I've managed to do some EEPROM hacking to enable some hidden functions on post-07-xx-yy 34401A FW, and one of the discoveries was a method for saving the EEPROM contents (inc. calibration table) without opening the case: https://www.eevblog.com/forum/testgear/hp-agilent-34401a-hidden-menu/msg4436983/#msg4436983

As of yet we haven't figured out how to write arbitrary values to the EEPROM without opening the case and connecting a programmer, but it may still be of interest here as at least you can get a quick backup. Would be best to whip up a script to do the work - I've already got my EEPROM dump from connecting a programmer to it, so haven't gotten around to writing one myself.

As for the hidden functions, tl;dr is that there are 3 EEPROM bits (plus a checksum update) that if set allow for saving and recalling mode settings etc. (inc. on power up), a temperature measurement option (thermistor, RTD or thermocouple) and finally a "SCALE" option in the maths menu that lets you scale and offset readings without involving a computer.