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Okay, my head is starting to hurt from all the banging against the wall... Can anyone explain how the "Shift-On" function works to display the time continuously? The code seems to sail right through the "POWOFF" instruction without stopping, and I don't know why. Thanks, Monte

Execute the CLOCK command to display the time continuously!


Can anyone explain how the "Shift-On" function works to display the time continuously?

You first press and release SHIFT (the solid yellowish key), "SHIFT" should be displayed on the LCD, then you press and release the ON key. Now your 41CX should display the time.

Unsure if this works with Time Module in 41C or CV (I do not have one to test).

I believe Monte is trying to figure out how the HP-41 works internally, not how to invoke the clock display.

Correct. I can't figure out why the machine doesn't stop with the POWOFF instruction, but continues on to display the time. There must be something I'm missing.

I have not checked the mode but i think there is a polling point called before the execution which could check for the key code Inc of shift key and divert the processor to a different point. For that i would look at the code in the last few addresses of the time module (the bespoke polling points)

I wish i had the time to check it out, it sounds like an interesting thing ti hunt down...



Just follow the TurnOff interrupt vector in the TIME module ROM;-)

I haven't disassembled it, but there is a big chance that this vector is used, and that the code behind starts the clock display routine if the SHIFT key flag was set...




Thanks, but the polling points are tested while the processor is running. The CPU executes POWOFF to go into light sleep after processing. I couldn't figure out how it started right back up. But after reading the spec for the timer chip (duh... rookie mistake) I figured out that the timer chip drives the ISA bus High, which is one of the wake-up conditions. Sorry for wasting everyone's time.