modular molded jack (DEC) (MMJ)
The MMJ connector is a modular connector used in DEC systems. The MMJ connector is a variant of the RJ connector, it is also made of transparent plastic, has six pins like the RJ12 connector and a locking mechanism.
The six connector contacts are occupied by transmit (2, 3) and receive (4, 5) lines, contact 1 is for Data Terminal Ready ( DTR) and contact 6 for Data Set Ready( DSR).