This is a work in progress and likely to be updated.
The HP67 Arithmetic, Control and Timing chip (ACT) is a Mostek MK6216N. It understands most of the instructions but the HP67 card reader chip (CRC, a Mostek MK6250N) adds instructions and two more data registers: Continue reading HP67 Card Reader
When the HP67 detects that a key has been pressed, it exits the HP67 Keypress Wait Loop and gets to instruction 0214 (octal). Then this happens: Continue reading The HP67 Keypress Routine
Woodstock was the name HP gave to its newer model processor for its newer model calculators at the time of the HP-67, HP-21, HP-25/C and HP-29. Here’s what was in it: Continue reading Woodstock Microcode
