HP41C ROM Addresses

[Mike T.]

Just trying to make some sense of the ROM layout on the HP41C.

I know that the HP41C has 3 ROMs ROM0, ROM1, and ROM2 which I believe are are located at page 0, bank 1, page 1 bank 1, and page 2 bank 1.

I'm not sure what the page size it but if the HP41 uses a page size of 4K then the starting addresses of each ROM would be 0000h, 1000h and 2000h. Is this correct?

I'll worry about optional ROMs later!!

Thanks

[rprosperi]

Each page is 4K or 4096 bytes, (000 - FFF). The first 'digit' of a ROM address is the Page (0-F) and keep in mind that ROM words* are only 10-bits. The extra banks came well after the CPU design was fixed, via other hardware on the CX board or in the module (e.g. Advantage ROM, HEPAX or ZENROM or MLDL, etc.) and so are somewhat invisible to the CPU addressing.

Other gurus that really know what they're talking about can expand on this and probably explain it better, but this should be enough to get you pointed in the right direction.

* Corrected, originally had addresses - doh! Thanks Monte!

[Monte Dalrymple]

Each page is 4096 10-bit words. ROM addresses are sixteen bits. The most-significant nibble selects the page. So yes, ROM0 starts at 0x0000, ROM1 starts at 0x1000 and ROM2 starts at 0x2000. As Bob says, banks were a later addition.

[Sylvain Cote]

Poul Kaarup's excellent HP-41CX Programmer's Handbook has several answers to these type of questions.

[Mike T.]

(04-06-2022 04:00 PM)Sylvain Cote Wrote:  Poul Kaarup's excellent HP-41CX Programmer's Handbook has several answers to these type of questions.

Another interesting reference I didn't know about!! The contents are a good deal more detailed than the title might suggest.

Thanks