CONNECTION DETECTING SYSTEM

PURPOSE:To detect whether an input/output controller or the like is connected or not while holding a low power consumption, by utilizing the floating state of a ternary signal output to fix bits of a data bus to a specific state. CONSTITUTION:In case that a processing controller 4 discriminates whether an input/output controller 8 is connected or not when general instructions (g), (h), and (i) are stored in an instruction storage register 9, a status read instruction (e) is stored in the register 9 through a data bus 3. Then, contents of the register 9 are substituted with instructions (h), (i), and (e), and the instruction (g) is transferred to an instruction executing device 10 and is executed. The controller 4 substitutes contents of the register 9 with dummy instructions f1, f2, and f3 holding the bus 3 in the H-level successively by a state fixing circuit 7, and instructions (h) and (i) are executed, and the instruction (e) is executed in a state (j). When the instruction (e) is executed, a reading circuit 5 reads the L-level or H-level output for connection or non-connection of the controller 8 on the bus 3 and sends this output to a discriminating circuit 6. The circuit 6 compares this output with a reference to discriminate whether the controller 8 is connected or not, and the result is reported to the controller 4.