A rather nice steel cased Gemini keyboard. It is actually a Cherry pcb bearing the number 7001-0066, tested 9/7/82. Unfortunately it appears to be faulty so some work is going to be needed. In the meantime, I’ve traced the circuit diagram for you.

GM821 keyboard circuit

The output of this keyboard is 7-bit ASCII with a positive-going strobe pulse.

Because of the restricted number of keys all codes sent are single-bytes. Links on the IVC and SVC cards allow the system to be switched between single (GM821) and double byte (GM827, GM852P) keyboards. The double-byte system is necessary to get the extra codes to handle the function keys.