JPS554682A - Addressing digital input device - Google Patents

Abstract

PURPOSE: To prevent the malfunction for the input device by detecting the output level of the channel selection circuit via the output level detection circuit, deciding the normality of the detection value through the fault detection circuit and thus detecting quickly the fault for the plural number of the channels.

CONSTITUTION: Channel control circuit 15 delivers the channel selection signals so that a number of digital data of the process are read in sequentially and every fixed time, and the input channels are set up in sequence by channel selection circuit CH. And the digital data selected by circuit CH and read in are memorized in memory device 11, and then read out to be sent to the external unit. Here output level detection circuit 12 detects the output level of circuit CH and monitors the operation of the output level, and the normality is decided by fault detection circuit 13 and based on the detection value of circuit 12. And in case some fault is detected, the alarm signal is delivered. As a result, the faults such as the simultaneous selection, the nonselection of plural channels and others can be detected quickly, thus preventing the malfunction.

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