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.
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