[volt-nuts] 3458A - To Modify or Not To Modify?

Poul-Henning Kamp phk at phk.freebsd.dk
Sat Nov 5 17:13:18 UTC 2011

In message <A429DA6E7F6843549CF0A35C3AF15508 at S0028384766>, "J. L. Trantham" wri

>However, perhaps there is a way to harvest the data by HPIB, archive it that
>way, and use HPIB to 'reprogram' new NVRAM's without the need to do a 'cal'.

There is.

You can read and write the entire address space using the MREAD and
MWRITE HPIB commands.

However, while you can just read the NVRAM with MREAD, you cannot
write it with MWRITE.

There are a number of safety circuits, which must be tickled just
the right way, to open the write signal to the NVRAM.

This is actually a really good design btw.  It's made that way to
protect the NVRAM contents from all sorts of bogons, such as saggy
power-supplies, glitches, software-bugs and so on, and it works.

I have tried, mostly for fun, to overwrite the 40k/7V cal constants
via HPIB on my meter, right before I unsoldered the old NVRAM.

You can do it, but you have to download (to an array), and execute,
a 68000 relocatable procedure which does the dirty deed for you.

If you can't write a 68000 program in assembler, this is not something
you should ever even think about attempting.

The entry points you need to call depends on the software version
of your meter, so you will get nowhere without a disassembly of
your firmware version.

If anybody ever gets stuck with absolutely no other sensible way
to fix bad CAL constants (as in "Yeah, I'm on the South Pole and
can send it to Agilent for cal when the next plane comes by, in 
six months time..."), I'll help them.

Until then:  Don't even think about it, but use an eprom programmer

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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