INTERFACE DEVICE

PURPOSE:To simplify input/output processing of a main computer by providing a common transmission line between the main computer and plural local computers and setting the use right to every local computer to transmit a signal. CONSTITUTION:The control input of a push-button switch 2A is received by a local computer 9A and is subjected to operation processings such as multiple selection prevention or the like and is encoded and is stored in an RAM13LA. The local computer 9A outputs an interlock signal from an output port 22LA for the purpose of confirming whether a serial transmission line 30b is used by other local computers 9B and 9C or not to transmit this control input to a main computer 1 through the serial transmission line 30b, and the interlock signal from other local computers is inputted from an input port 21LA; and if the use right of the serial transmission line is obtained, the control input is converted to serial data and is outputted from a transmitter 14LA.