[volt-nuts] HP3458A calibration memory backup

[Mark Sims]

I have three HP3458A's and decided it was time to back up the battery backed static RAM chips.  I wrote a program to dump the RAM contents over the GPIB bus using the undocumented MREAD command as documented by Poul-Henning.   I dumped both the 2kB CAL rams and the 32kW auxiliary data RAMs (hopefully that data is at the addresses mentioned by Poul-Henning.   I used a NI GPIB-232CV-A RS232 to GPIB converter as the interface.   All seems to have gone well and the CAL data looks reasonable.
As a check I dumped all the data from each machine three times and compared each dump...  each CAL data set matched except for the third machine.   On the first two,  the units were powered on for a couple of hours while I tweaked with my code.  I dumped the third machine from a cold start and one byte was different between each dump.  I waited a couple of hours and tried again,  this time the data dumps matched.  It looks like that byte may be being updated while the machine warms up...  If you dump your machine's data,  it might be a good idea to let it stabilize for a couple of hours first.
The dumps of the 32kW of aux data have several words that change between each dump.  It looks like that memory has some uses by the firmware other than storing user data, etc.
I think when the time comes to replace the battery backed memory chips I may try Cypress/Ramtron FRAM chips or Simtek STK16C88 AutoStore devices.   The Simtek chips are available in 28 pin DIP packages that appear to be drop-in replacements for the DS1230 chips.  The DS1220 chip would require a SO8 packaged part on a carrier board.