PURPOSE: To read various copying states by connecting an interface board to the RAM socket of a copying machine control board and enabling the transmission and reception of data, and using a dual-port RAM on an adapter side for a communicating means and sharing some addresses of the RAM.

CONSTITUTION: The interface board is provided with pins so that it can be connected directly to the RAM socket of the main control board of the copying machine. A RAM which serves as the RAM on a main control board and a bus driver/receiver for interface with the RAM are mounted on the interface board. When A3WA10 are all H, the RAM on the interface board is inhibited from being accessed and switching to the dual-port RAM of a microcomputer on the adapter is performed. The high-order byte addresses of the RAm are assigned on the dual-port RAM. Then, the computer side transmits and receives data to and from the adapter as well as the reading and writing of the RAM. Consequently, a data communication can be made without altering the control board of the copying machine.