| 摘要 |
PURPOSE:To readily detect a contact failure, by a method wherein, using a binary- coded decimal notation code which is readily inputted to a 4- or 8-bit microcomputer, and with the 4-bit form being left, a contact failure code is overlapped with the 4 bits. CONSTITUTION:If the digital switch now selected has a contact failure, the potential of the current flowing through the selected one of resistors R0-R9 from a voltage source Vcc will not drop because of the contact failure of the switch. Consequently, the inputs of an encoder 1 are all H, and the outputs thereof 0. After all, the output from an NAND circuit 2 through an inverter circuit 3 is H. Accordingly, since one input H is applied to each of ''OR'' else circuits 4a-4d, they output F as the inverted form of the output 0 of the encoder 1. In other words, when the digital switches are normal, 0-9 are outputted, and when there is a contact failure, F is outputted. By such a constitution, a contact failure can be readily detected. |
