Unused registers on 67 and 97
11-07-2022, 01:04 PM
Post: #1
 teenix Senior Member Posts: 1,685 Joined: May 2016
Unused registers on 67 and 97
Hi all,

I think I got Flu or Covid from visiting my grand-daughter who was coughing relentlessly, and have been quite ill for a week or so, bless her little soul, but I'm sick of being sick so I tried to get the brain working again today.

As per the mention of the non-use of these registers for the 67 and 97 in this thread, I decided to see if they can be utilized in anyway. There are located at addresses $3A,$3B and \$3C.

There is very little spare code space left in these calculator ROMs, (about 8 useable words) so I wasn't optimistic about being able to do anything. There is also another 8 in Bank 1, but to use them, the code must be executing in Bank 1 already.

As luck would have it, I did manage to make use of these RAM registers by using 7 of the spare ROM words. This mode can be enabled/disabled on the Teenix 67 emulator, which changes the assembler files, and when enabled, by using the RAM swap keys [F] [P<>S], 13 registers are swapped instead of the usual 10.

Indirect addressing for these 3 registers still doesn't work, but either way, there is no more ROM to make any further changes unless it is a simple modification.

I'll do the 97 emulator soon and then try and give the option on the CPU boards.

cheers

Tony
11-07-2022, 07:59 PM
Post: #2
 brouhaha Member Posts: 285 Joined: Dec 2013
RE: Unused registers on 67 and 97
Nice work!

In my attempts at 67/97 firmware hacking, I haven't tried to maintain the ROM size. I've added additional bank 1 ROM. Getting more program steps by relocating the secondary and status registers is not too difficult, but expanding the available indirect registers takes more work, and I haven't yet started on card reader support for larger programs.
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