RPN-65 Question.

[Steve Simpkin]

(08-21-2023 12:30 AM)teenix Wrote:  From the emulator, RAM [20] and [21] are used for trig calculations and RAM[22] doesn't appear to be used for anything. This is strange as I thought with the cost of chips in those days, it would have some use.

RAM[20] stores the Last X value too, so if you do a trig function, the Last X is lost. I wonder why RAM[22] wasn't used for Last X then.

I suspect there just wasn't enough ROM to code in a different address for Last X using RAM[22], as the Microcode that sets up the address for RAM[20] is a common routine between trig functions and Last X.

cheers

Tony

Tony, can you check that again? Using your HP Classic Emulator for PC (an Awesome program!) for the HP-55 it looks like RAM[21] is used as a scratch register during trig calculations but RAM[20] always has the correct Last X value in it even after a trig operation. Also in use, the Last X function seems to work as it should even after a trig calculation.