Use PC serial port to read 16 digital input channel circuit diagram

The RS-232 serial port has 4 input lines (pins 1, 6, 8, 9) that are accepted by two dual 4-input multiplexers ( IC 1 and IC2) for 16 channels of input, and two output lines (pins 4, 7 ) controls the input channel selection. Each line allows the PC to read 4 input channels under the control of the C program. Pin 4 powers the IC through VD and charges C1. When pin 4 is low, C1 keeps supplying power to the IC . VDW1 and VDW2 limit the output voltage to -0.6~+5.1V.
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