Failure detection in an analog-digital conversion function of a microcomputer

摘要

In a microcomputer 10 including an output port 20 for outputting digital signals and an AD conversion register 18 for converting an analog voltage inputted to an AD input port 16 to a digital signal, the output port 20 and the AD input port 16 are directly connected. The output port 20 is allowed to selectively output H of a power source potential and L of a ground potential. The AD conversion register 18 is judged as being failed when any one of predetermined high order bits of the AD conversion register 18 is not 1 at the H output, or when any of one of the predetermined high order bits is not 0 at the L output. The digital conversion value of this AD conversion register 18 is not used. Thereby, existence/absence of failure of the AD conversion register is detected without using 2 channels for the AD input port. <IMAGE>