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HP / Agilent 34401A hidden menu

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robert.rozee:
i'm afraid i'm a little late to the party here. i do have a 34401A, but not one that i can tinker with. nonetheless...

regarding the two HP poke commands to enable/disable the 10mA AC range:
"DIAG:POKE 25,0,1"
and
"DIAG:POKE 25,0,0"
can someone post screen dumps (before and after) of what the EEPROM looks like, like the one TV48 posted in reply #65 above? preferably with any changed values highlighted?

if the 10mA AC pokes change one bit, then it seems that either the necessary checksums are automatically updated, or TWO bit locations are updated, so that one change cancels out the other when calculating any checksums.


cheers,
rob   :-)

Hydron:

--- Quote from: tv84 on September 25, 2022, 12:08:01 pm ---Can you try to disable the Temp by using the POKE 25 as I hint above:

POKE 25, 3, 0

--- End quote ---
Still only changes the 10mA AC range (turns it off). TEMP stays on.

@robert.rozee:
The POKE 25 commands only seem to change the bit for 10mA AC range (a single bit), but as you assumed, the checksum is then automatically updated (so I guess you could say it changes more than just the single bit, but the checksum only determines whether the meter throws an error).

robert.rozee:
so we can change the parameters to "DIAG:POKE ..." and observe how they change the EEPROM dump? ie, instead of the two we know: "25,0,1" and "25,0,0", we could try (for instance) "25,0,2", "26,0,1", and other minor variants - although initially at each step changing just a single parameter.

in a sense, we know the outcome we seek. now we just need to reverse-engineer the behavior of "DIAG:POKE ..." to figure out how it affects the pattern saved to the EEPROM.


cheers,
rob   :-)

Hydron:

--- Quote from: robert.rozee on September 25, 2022, 12:28:26 pm ---so we can change the parameters to "DIAG:POKE ..." and observe how they change the EEPROM dump? ie, instead of the two we know: "25,0,1" and "25,0,0", we could try (for instance) "25,0,2", "26,0,1", and other minor variants - although initially at each step changing just a single parameter.

in a sense, we know the outcome we seek. now we just need to reverse-engineer the behavior of "DIAG:POKE ..." to figure out how it affects the pattern saved to the EEPROM.


cheers,
rob   :-)

--- End quote ---
I had a crack at this already - see my first post in this topic (probably on page 2). Didn't have much luck with this, and it was time consuming, as I had to go back through the logic analyser output after each test to look for write commands.

If you have the ability to write an EEPROM in case of disaster (seeing as we don't have the command for arbitrary write yet) then feel free to write a script to dump yours with the PEEK command I just discovered (or just using the programmer), and have a play.

tv84:
The 3rd param of POKE 25 looks like it's ON (1) and OFF (0).

IMHO that should not be necessary to brute force anymore.

Assuming that this POKE 25 is the one for all options, I would bet on testing plenty of 2nd params to see if they are responsible for other bit positions (in the options bytes).

BUT AFTER HAVING A BACKUP DUMP.

As Hydron has tested, I don't thing other POKE numbers (26,, 27, etc) will do the trick...

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