There are many I/O circuits in the DSMB-01C, one for each input or output point, and there are generally as many I/O circuits as there are I/O points in the PLC. However, since they are composed of highly integrated circuits, they do not occupy a large volume.

The DSMB-01C input circuit monitors the input status at all times and stores it temporarily in the input register. Each input point has a corresponding register that stores its information. The output circuitry has to transmit the information from the output latches to the output points. The output latches are also one-to-one with the output points.

The DSMB-01C’s input registers and output latches are actually the registers of the PLC processor’s I/O ports. They exchange information with the computer memory through the computer bus and are mainly realised by running the system program. The information in the input registers is read into the PLC memory, called input refresh, and the PLC memory has a special mapping area for input information. Each corresponding bit in this area is called an input relay, or soft contact. These positions into 1, said contact pass, set to 0 for contact break. Since its state is refreshed by the input, it reflects the input state.