Posts: 528
Threads: 85
Joined: Jul 2005
That is simple, just use the PWO signal to control power to the LED. PWO is high when the calc is running. You could also make a wired OR (with two diodes) to have the LED on when running and when in STANDBY.
To control power make a simple FET switch or transistor, or drive a LED directly if it does not draw too much power.
Drive a multicoloured LED would really require more complicated stuff. My MLDL2000 can drive LED's by choice with access to reserved memory locations. Cheapest solution would be a Novram like device with some spare I/O. It would be fun for amateur astronomers to read the current time and date to check if the sun has set already and then drive the red LED ...
Meindert