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HP-41: upper bits in module ID fields
04-14-2020, 08:18 PM
Post: #1
HP-41: upper bits in module ID fields
HP-41 modules has a four character ID field at address 0xffb-0xffe, used to identify the module and version, i.e. AD1B.

Normally the values stored here are low numbers and HP defined the 0xffd word to also carry a flag if the module is banked. This is done by setting any of the upper two bits (of the 10-bit word) to non-zero.

I now need to allocate another flag like this and picked the 0xffe word for this purpose. Is this a "safe" thing to do?

After running through some modules I found a couple that actually store non-zero bits in that position. Advantage module puts 0x201 (letter A with one of the upper bits set). Real Estate stores 0x100 there. SandMath 4x4 stores a lot of upper bits in the whole ID field area and it varies a bit when I dig deeper into the pages.

Was the upper bits in 0xffe ever defined to mean anything? HP does have a couple of modules that use it. Why does SandMath sprinkle in values like this in the ID area?
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HP-41: upper bits in module ID fields - hth - 04-14-2020 08:18 PM

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