[volt-nuts] HP3458A calibration memory backup

[Todd Micallef]

Mark,

I am using the STMicroelectronics M48Z12 series in at least one of my
3458A's. I had trouble sourcing one of the two different memory modules
from a reputable seller when I replaced my NVRAM. I purchased a DS1220
previously from Jameco and it died shortly afterward. The datecode on the
Jameco part was several months old and may have been stored improperly.

The only thing I don't like about the STMicro NVRAM is that they use a
three digit datecode. One digit is for the year and two for the week. It
took me a while to track down a document to decipher their labeling system.

Todd




On Thu, Aug 7, 2014 at 12:20 AM, Mark Sims <holrum at hotmail.com> wrote:

> 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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