8-way switching input interface circuit

The circuit circle of the 8-channel switching input interface is given. It can be seen from the figure that the switching signals sl~s8 are used to control the light-emitting diodes of the optical coupling
device to turn on and off. When the switch is closed, the LED lights up, otherwise it goes out. The phototransistor is driven by coupling,
sending a high or low level to the collector of the transistor accordingly . After using photoelectric isolation, the external interference caused by the input end can be effectively overcome. The computer reads
the 8-bit switch signal into the CPU through the effective address (/cs) and the read command (/column∞, ) .