The M in the PLC is called the auxiliary register.
To realize the identification and processing of the on/off and level status information of each interface, the PLC must convert them into variables that can be recognized by the internal computer. These variables are called registers.
According to different models of PLC, commonly used registers
(1) Input register (X/I) – Saves the status of each input interface.
(2) Output register (Y/O) – saves the status of each output interface.
(3) Auxiliary register (R/M). The auxiliary register, also known as the intermediate register, is used to store the state of the intermediate variables required in the operation. The role of transmitting signals in the PLC