LED on PET motherboards.

[Shaun_CCC(UK)]

Hi,

We're working on a restoration project for the National Museum of Computing here in the UK (http://www.tnmoc.org) and we were wondering what the red LED is supposed to do when you switch the machine on? Is it supposed to flash, light up, light up during boot up etc...

Can anyone help please?

Regards,

Shaun.

[pet1978]

Hi


The LED will only light when running Commodore's diagnostic software. It is turned on by a normally unused keyboard scan-line value. Official Commodore dealers had a small box that was clipped onto the CPU which contained the diagnostic software in ROM.


Schematic (LED is near bottom right corner, driven from E9 NAND gate): http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001/320130-1.gif


Dave