INTERFACE DEVICE

PURPOSE:To simplify the input/output processing of a main computer by constituting a common transmission line between the main computer and plural local computers, setting the use of right at each local computer and transmitting the signal. CONSTITUTION:The main computer (MCP) and plural local computers (LCP) are connected by a common transmission line 30. when a control signal is inputted to each LCP from a switch, it is stored in a control signal input storage means A. A transmission line state detection means B inputting a signal from the transmission line 30 discriminates whether or not other LCP uses the transmission line from the state where the input signal repeates on/off at a prescribed period and sets the use of right of the transmission line 30 when the other LCP is not in use, and a control signal stored in the means A is fed to the MCP from a transmission signal output means C. A transmission signal input means F of the MCP receives a signal from the LCP, it is checked by a transmission signal check means I and a confirming signal output means H transmits a signal whether or not the reception signal is normal to the LCP.