HP-91 OOPs

[teenix]

The 91 and 92 are basically an identical setup except for the switches. Internally though, they connect the same to the ACT.

Also, the 92 has a different key matrix. I don't know why they would bother designing a circuit board different than the 91 given that they have the same key layout, but maybe the microcode needed different key codes to function properly or was easier to code for.

In all Topcats, the paper advance switch is detected by the ACT, but the 91 appears to have a special instruction to tell the PIK chip to print a short blank line when the paper advance key is pressed, whereas the 92 and 97 execute normal printing PIK codes.

cheers

Tony