3421A CAL RAM

[J-F Garnier]

(04-02-2017 05:24 PM)Dave Frederickson Wrote:  ... The 3468 cal data can be read as a 255 character string using the B2 command, per the label on the bottom of the DMM....

Please share your cal data. Mine's corrupt so I'd like to see what good data looks like.

That reminds me, I need to order another battery.

Thanks, Dave

That for the B2 hint! I just experimented with it, and yes, the HP3468 sends 255 (not 256) characters following the B2 command.
Here is my HP71 program:
10 !
15 DIM A$[256]
20 A=DEVADDR("HP3468")
40 REMOTE
50 OUTPUT :A ;"B2"
60 ENTER :A USING "#,255A";A$
70 DISP A$

and the result is:
@@@@@@@@@@@@OOOO
IIIIII@@BMOKODLH
@@@@@@@@BLL@OMML
@@@@@@F@BM@OOILO
@@@@@@@@BLMNOBM@
@@@AFGC@L@LOOCNK
IIIIIIF@NBMDOLLC
@@@@BDA@ACCOI@EC
@@@@@@@@AA@COLLO
@@@@@@@@ABCKODLH
@@@@@@@@ANBNOLLC
@@@@@@@@ALNKOGM@
IIIIIIDANMMLOH@D
@@@@@@@@@@@@OOOO
@@@@@@@@@@@@OOOO
@@@@@@@@@@@@@@@

I added the line breaks each 16 bytes manually for clarity. Note the missing character is the last line, since there are 255 characters.

Observations:
all bytes are regular ASCII characters, which makes the manipulation of calibration data easier,
the characters are all in the range @-O that is 16 values: each calibration byte holds a 4-bit nibble,
there is no visible checksum.

It may be that the checksum is held in the 256th location of the calibration RAM and is not transmitted in the B2 response.
We can imagine that the B3 command to write calibration data also asks for 255 bytes and automatically adds the checksum.
I don't want to try - don't want to risk to corrupt my HP3468 calibration - but maybe Dave can you try ? :-)

J-F