HP-41CX w/ XF-Module - just curious

[rprosperi]

(07-26-2019 04:36 AM)Ángel Martin Wrote:  The BUS search order is dictated by the mainframe MCODE. It always starts at page 5, moving up until page F. When the CX was released HP added a new page at the END of the search, page #3 - that's why 3 in the CAT 2 is shows the last.

So when you XEQ EMROOM, the OS finds the XROM #26 first corresponding to the external X-Funct module. It scans that FAT and notices that the id# in question is not there, so it puts out NONEXISTENT - without continuing the search along the BUS and threfore never reaching page #3 (the "last" one).

The same happens if you plug two different modules with the same XROM id#, and the first one has fewer functions than the second: only functions from the first one are found.

It's all in the MCODE ;-)

Cheers,
ÁM

Thanks very much Angel for the explanation. Like so many things, it makes perfect sense once someone has explained it to you! I did not consider that the XROM search halts when reaching the end of the first ROM with matching XROM number, but as you say it makes sense, since one is not supposed to install more than 1 ROM module at a time with the same XROM # (as in all the "X" modules HP released).

And I suppose HP added Page-3 at the end of the existing C/CV CAT-2 search, as it was simply easier to just add this onto the end of the existing code. I have always wondered why the CX shows XFM and CX XFM at the end of the CAT-2 listing.

Thanks for clearing up these mysteries!

My view is slightly different than yours - It's all in Angel's head!