HP-41: upper bits in module ID fields

[Ángel Martin]

Here's the text in the ZEPROM manual, never mind the references to "cores" (something only ZEPROMS have), but see the bold sentence included:

"The ZEPROM hardware initially determines the configuration is bank-switched or
straight from the two most significant bits of data at address location xFFD in core 1. If
both bits are clear, then the module is considered as straight 16K. If either or both bits
are set, then the module is considered as being bank-switched. In a bank-switched
configuration then either one or both of the two most significant bits of the data at
address xFFD in core 3 should also be set. If this is not done, then ZEPROM will be
able to select the secondary bank, but will not be able to return to the primary bank.
The use of the most significant bits of address xFFD complies with the bank-switching
convention established by Hewlett-Packard; in which any bank switching page will have the most significant bit of the data at address xFFD in that page, set. Remember however that ZEPROM only references the bits in core1 (and core 3) to determine if the entire ZEPROM is bank switching. The PROGRAMMER ROM software also uses an extension of the HP convention to determine if a page is bank-switched and also which page is currently selected"


That was back then but later on the HEPAX introduced a more capable Bank-switching scheme (added two more banks to the picture), so my guess is they extnded the x0FFD conventions also to xFFC and 0xFFB - which should infer that using 0xFFE is a safe option for HEXEDIT though...

ÁM