Rs232 was achieved with the local port going to the ERS board. It was also capable of 20ma current loop to a teletype depending on pins used.
The large connector on the ERS must be pulled and left hanging for RS232. Baud rate is set by DIP switches on the ERS.
The tape reader used a parallel interface. The BTR is used in place of the DNC loader for large programs exceeding the machine memory.
There is a LOT of data on this forum about all of this. Just search for it.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)