The M Register is one of the general purpose registers within the relay computer. It can hold two 8-bit values (M1 and M2) and can read and write from/to the data bus.
Additionally it can also write (but not read) a 16-bit value to the address bus combining the M1 and M2 8-bit registers together.
Below is a list of the blog articles relating to this card (in reverse date order):
