Electronics > Repair
HP 3478A: How to read/write cal SRAM
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dfrederickson:

--- Quote from: MarkL on April 06, 2017, 09:48:02 pm ---Well, and then there's always the brute force method.  If you're right that there's only 16 bits of ECC, how long will it take to write and test all the possible ECC values (or half, on average)?

--- End quote ---

Hi MarkL,

I don't know, but the Infinite Monkeys Method worked before. :)  The 3468 is basically an HP-IL version of the 3478, minus a few extra ranges and rear terminals.  The 3421 is a data acquisition instrument that employs a 5.5digit DMM, similar to the 3468 and 3478, but with no front panel controls.  The 3468 and 3421 are highlighted in the Feb 83 issue of the HP Journal and the 3478 got an honorable mention.

True, it would be easy to write a program that sequentially tried all the different checksums until a status error was not reported.  I'll think I'll wait until someone like Sailor simply figures out the algorithm.  In the mean time I can load parameters from another 3468 and clear the error.  For now that should be accurate enough for what I'm doing.

Regards, Dave

biot:

--- Quote from: MarkL on April 03, 2017, 02:33:56 pm ---It would be nice if someone could write a python or some other multi-platform method that implements the above in a friendly way.  There's a lot 3478A's out there.  It would make battery replacement a lot less stressful if you could back up the SRAM first and then restore it when done.  No more isolated soldering irons, etc.  Or even better, it would be good to make a backup *before* the battery goes dead.

--- End quote ---

I'm attaching a little Python script that pulls the SRAM values out and drops them to stdout. Use like this:

python cal-3478a devicename > mycal

This depends on a properly working linux-gpib setup, and devicename must be a properly configured device in /etc/gpib.conf. No multi-platform GPIB out there, as far as I know.

Thanks so much for working this out -- would hate for my 3478A to die on me. At least now I have a backup! The battery seems to be doing OK, so perhaps I don't need to replace it yet?
MarkL:

--- Quote from: biot on April 09, 2017, 04:07:22 pm ---
--- Quote from: MarkL on April 03, 2017, 02:33:56 pm ---It would be nice if someone could write a python or some other multi-platform method that implements the above in a friendly way.  There's a lot 3478A's out there.  It would make battery replacement a lot less stressful if you could back up the SRAM first and then restore it when done.  No more isolated soldering irons, etc.  Or even better, it would be good to make a backup *before* the battery goes dead.

--- End quote ---

I'm attaching a little Python script that pulls the SRAM values out and drops them to stdout. Use like this:

python cal-3478a devicename > mycal

This depends on a properly working linux-gpib setup, and devicename must be a properly configured device in /etc/gpib.conf. No multi-platform GPIB out there, as far as I know.

Thanks so much for working this out -- would hate for my 3478A to die on me. At least now I have a backup! The battery seems to be doing OK, so perhaps I don't need to replace it yet?

--- End quote ---
The python script works for me and the data matches my clunky scripts - thanks!

I haven't replaced my battery yet and it's now 34 years old.  As long as you have a backup, my feeling is not to worry about it.  If one day you turn on your meter and the battery is dead, you can reload the calibration constants and still use the meter while waiting for a new battery.

Of course it's then time to write the SRAM writer script, or even better write it ahead of time.  If you want to PM me a test version I'll try it - I'm not afraid if it takes a couple of spins to get it right and it ruins my constants.  Once right you can post it.
bingo600:
@MarkL et all

Now we "just" need to reveal the HP3457's secrets   ;)   

PHK did the 3458A , and you did the 3478A
Who's doing the 3457A

/Bingo
MarkL:

--- Quote from: bingo600 on April 12, 2017, 07:46:14 am ---@MarkL et all

Now we "just" need to reveal the HP3457's secrets   ;)   

PHK did the 3458A , and you did the 3478A
Who's doing the 3457A

/Bingo

--- End quote ---
Sounds like a fun challenge, but unfortunately I don't have a 3457A.

I did look at the ROM image that's available on KO4BB with "strings" and "xxd".  It looks like there's a ROM monitor that can be accessed somehow.  That might provide a path to read/write the NVRAM (U511).

There's also some occurrences of the words PEEK and POKE in the same area as other GPIB commands.  That looks promising but they might need to be enabled first.


I doubt it will happen, but if anyone wants to lend me a 3457A for a few weeks I'll give it a shot.  I already have a 3456A, so I don't have a good excuse to buy one myself (not to mention making space for another gigantic DMM).
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