Applies To:
  • CitectSCADA 3.xx, 4.xx, 5.xx

What does "Maximum Request Length" mean? 

Maximum Request Length is the maximum number of data bits that can be read from an I/O Device in a single request. For example, if the maximum request length is 2048 bits, the maximum number of integers that can be read is: 2048/16 = 128

If you define an array of I/O Device variables, you must ensure that the array does not exceed the maximum request length.

The Maximum Request Length (Max_Length) for each protocol can be found in the Protdir.dbf file in the BIN directory, and is also documented in the Citect online help for each protocol. The value of the Maximum Request Length is usually limited by the protocol, although Citect also has a limit of 2048 bits irrespective of the protocol.