TIMER CIRCUIT PROVIDED WITH SELF-DIAGNOSTIC FUNCTION

PROBLEM TO BE SOLVED: To easily confirm whether timer counter operation is normal or abnormal by incorporating a function for detecting the counter operation being abnormal according to the result of logical operation between the time of the timer counter circuit and a specific value. SOLUTION: In self-diagnostic function test mode (CNTTST='1'), input capture circuits 2 and 3 used in normal mode hold the counter value at (tn+1) time and counter value at tn time of the output of the timer counter circuit 1. In this case, an AND ALL '0' detecting circuit 4 ANDs the uninverted value at (tn+1) time and the inverted value at tn time to judge normal +1 count operation when the result is '0' and abnormal count operation when '1'. Then it is judged whether a clock is in operation or at a stop from the output level of a set preferential R/S flip-flop circuit 8 and when the operation of the timer counter is disabled, the clock signal for the timer counter stops.