SR area (231 ~ 255) is divided into the first two parts
232 ~ 251: often used as a channel unit
232 ~ 249 does not make the specified function in the table, can be used as auxiliary relay
250,251 can only use the function in the table, can not be used for other purposes.
252 to 255 for storing the operating state, generating a pulse signal, and the like.
In addition to 25200, the 252 to 255 state can only be used, can not be changed.