HP 11C internal number format?

[Michael Zinn]

Hi,

I'd like to know what is going on inside registers and on the stack. How are numbers represented internally? Is it decimal or binary? How precise is it? How does rounding or other numerical things behave?

Thanks.

[Dieter]

(03-17-2018 08:03 PM)michaelzinn Wrote:  I'd like to know what is going on inside registers and on the stack. How are numbers represented internally? Is it decimal or binary? How precise is it? How does rounding or other numerical things behave?

The basics are covered in this article on the museum website.

Most internal arithmetics are done in 13-digit precision which finally are rounded to 10 digits before they are returned to the display. A common method is adding 500 to the last three digits (11...13) and then return the first 10 digits.

Dieter

[Michael Zinn]

Thank you, that is very helpful.

[Dieter]

(03-17-2018 10:05 PM)michaelzinn Wrote:  Thank you, that is very helpful.

You may try Warren Furlow's V41 emulator (HP-41CX) which has a very nice machine code console. Here you can see the internal microcode at work. But some patience is required: a simple "LN" or "SIN" may take hundreds of CPU commands until the result is returned. Try a simple addition first. ;-)

Type 2 [ENTER] 3, then options > console, check [x] Run and press the [+] key. You can see the LCD go blank and the "+" appear (the '41 briefly shows the command name if the respective key is held down), then the internal registers are loaded with 2 and 3, eventually the result 5 shows up and the result is written to the display again. If you do a division you can also see the internal roundoff routine at work. Hint: there is a slider to control the execution speed.

Dieter

[ggauny@live.fr]

Hi Dieter,

Many thanks for the link. A really HP 41cx !
I've already two HP 41, one is C and the other is CX, both are running.

Good day.