Applies To:
  • CitectSCADA 1.00, 1.01, 1.10, 1.11, 2.00, 2.01

Question: I am writing a Citect serial protocol driver and need to know what is the buffer size for the COMXi, PCXi and MCXi Digiboards.  

Answer: The transmit and receive buffers sizes for all the Digiboards drivers and the Com port is 1600 bytes each. You can transmit bigger packets but when this buffer becomes full Citect will do a hard wait to put any extra characters into the buffer. This will greatly reduce performance, so you should limit maximum packet size to less than 1600 bytes. The buffer sizes have been designed for a maximum packet size of 1024 bytes, so one and a half packets can be contained in the receive buffer before an overflow will occur. Overflows would only occur when the protocol driver is very busy, and cannot remove the packet fast enough from the buffer before a new packet arrives.