The SR area (231~255) is divided into two parts
232~251: often used in units of channels
232~249 can be used as auxiliary auxiliary relay when no specified function is specified in the table
250, 251 can only be used according to the functions in the table, it can not be used for other purposes.
252 to 255 are used to store working status, generate pulse signals, etc.
Except for 25200, the status of 252 to 255 can only be used and cannot be changed.
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