42s - That other 28pin footprint?

[TomC]

I don't believe this has been covered before; if so, please direct me there!

I'm 'fixing' the display in my 42S (missing columns/rows) and thought I may as well upgrade to 32K.

While inside, I've been reminded of that other 28pin footprint next to the memory IC.

Any speculation what this was intended for? Can it be utilized now?

Thanks in advance,
TomC

[Paul Dale]

This has been investigated before. I can't locate the source at the moment.

The extra pads will accept a memory chip (ROM) and I think there is one command which can transfer execution to the new chip but nobody's managed to do anything useful with it.


Pauli

[Sylvain Cote]

FYI ... Takayuki HOSODA has publish several modifications made to his HP-42S HERE

[Didier Lachieze]

(09-03-2016 08:34 PM)TomC Wrote:  Any speculation what this was intended for? Can it be utilized now?

The second 28-pin footprint was used for a second ROM in the HP-17B/BII international versions which contain different languages in addition to english.

See the discussion starting with message #7 here for details about using this slot in the 42s.

[TomC]

Thank you all!