| 摘要 |
PURPOSE:To eliminate an artificial accident and to shorten the time required to confirm whether or not there is a response to an instruction by counting the I/O address of each communication control unit by the counting circuit in a central processor and setting the value automatically in the register circuit in each communication control unit right after a system is reset. CONSTITUTION:The I/O address counting circuit 101 of the central processor 1 starts counting up with a clock signal CP after the reset signal of the system rises, and its outputs CA0-CA3 are sent out to the respective communication control units 2-5. Register circuits 201 of the control units 2-5 latch the values of the CA0-CA3 from the central processor by one of STB0-STB3 corresponding to the control units to set an I/O address corresponding to the control unit. Further, the setting of the I/O address in the register circuit 201 is ANDed with its strobe signal STB and a response signal RES is outputted. Consequently, there is no response signal if the I/O address of an unmounted communication control unit 4 is set, so software knows the mounted/unmounted state at any time.
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