JPS57207902A - Input circuit of controlling device - Google Patents

Abstract

PURPOSE:To reduce the number of level converting circuts so as to minimize the size of the device, by installing level converting circuits for detecting abnormality which are commonly used for numerous input contact signals. CONSTITUTION:An input circuit is constituted in such a way that level converting circuits 9 and 10 for detecting abnormality are commonly installed for each signal input contact 1a-1n, and instantaneous inputs of the contacts 1a-1n are inputted into the circuits 9 and 10 through contacts 1a-1n are inputted into the circuits 9 and 10 through diodes 11a-11n for preventing reverse current, and the output of the circuit 9 is made as a common input of comparators 5a-5n, and then, outputs of the circuits 9 and 10 are compared with each other at a comparator 12. The comparator 12 is constituted in such a way that, when the input is different from the proper one, it sets an FF 13 and closes all gates of AND gates 14a-14n equipped with inhibit input which correspond to each contact 1a-1n, respectively. Outputs of level converting circuits 2a-2n and the circuits 5a-5n which correspond to each contact 1a-1n, respectively, and the output of the FF 13 are inputted into the gates 14a-14n. When input signals of the circuits 5a-5n are different from proper ones, the outputs of the of the gates 14a-14n become ''0''. Moreover, when an abnormality is detected at th comparator 12, it is decided that whether the input signal is normal or abnormal by setting the outputs of the gates 14a-14n.