ANALOG INPUT/OUTPUT DEVICE

PURPOSE:To improve the responsiveness and the reliability by quickly performing A/D conversion with a loop of a comparing means, a microprocessor, and a D/A converter. CONSTITUTION:An analog input/output device consists of a microprocessor 1, a D/A converter 2, a signal holding circuit 3, a multiplexer means 4, and a comparing means 5. A first switch SW1 controlled by the microprocessor 1 is provided between the D/A converter 2 and the signal holding circuit 3 and is connected to the side of a contact (a) at the time of A/D conversion and is connected to the side of a contact (d) at the time of D/A conversion. The microprocessor 1 performs A/D conversion of a prescribed reference voltage inputted through the multiplexer means 4 by the A/D conversion loop and obtains a span by the result. The microprocessor 1 outputs two kinds of digital signal different in value to be outputted and subjects them to A/D conversion and obtains the error direction of the gain. Thus, the error due to the variance of the gain of the signal holding circuit 3 is corrected to correct the output error.