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HP-41CX w/ XF-Module - just curious
07-25-2019, 01:00 PM (This post was last modified: 07-25-2019 05:01 PM by rprosperi.)
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RE: HP-41CX w/ XF-Module - just curious
(07-25-2019 12:44 PM)burkhard Wrote:  Which brings us to to the narrow question:
→So... Would the Extended Functions / Memory Module plugged into a CX add any Extended Memory? Would the user now have 248 (=2×124) extended registers?

The following is theory and has not been tested.

The extra RAM is there of course, but cannot be accessed. The storage RAM in the CX is managed (initialized, read, written, etc.) by the code in the CX ROM, the storage RAM in the XFM (in a C/CV) is managed by the code in the XFM ROM, which is port-addressed.

Since the CX ROM is always in a lower port than the XFM ROM, this code will always be accessed first and will only manage the RAM it is aware of; the RAM in the XFM has never been initialized so cannot be recognized.

To be verified...

UPDATE: The above theory is NOT fully correct, but it does not change the basic answer.

With programs in CX XMEM, I installed an XFM. Doing a CAT-4 shows a corrupted file chain with jibberish characters in filenames and the catalog repeats the same files, but upon exiting, shows no increase in available XMEM (i.e. same amount free as before adding the XFM).

What is also interesting is with the XFM module installed, the EMROOM command is not found (EMROOM is one of the CX's added Extended Mem commands), so the above discussion of ROM addressing seems to not be fully correct either, so something more subtle is going on...

Bottom line is no, adding an XFM module to a CX does not provide additional Ext RAM for storage.

--Bob Prosperi
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RE: HP-41CX w/ XF-Module - just curious - rprosperi - 07-25-2019 01:00 PM

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