Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01

Question: I am getting the Hardware error "Request timeout from I/O Server". What is the exact meaning of this error and how can I fix it? 

The "Request timeout from I/O Server" error is generated when a Citect client has send a request to read or write PLC data to the I/O Server and the I/O Server has not completed the request within the LAN Timeout period. The LAN timeout period is controlled by the parameter [LAN]Timeout and with a normal LAN will default to 8,000 ms. If you are using CiNet the LAN timeout period will be extended to default to 60,000 ms.

Under normal operation with most protocols every Citect client should expect all its requests for PLC communication to complete within the 8 second default timeout period. If you have a very heavily loaded system with a slow protocol driver it may take the I/O Server longer than 8 seconds to process all the requests. This error may also occur when you have some other problem with your PLC communications which is causing slow response times.

First check that the communication to all the PLC is operating correctly and fix any errors. If the communications to the PLCs are operating correctly then you may just be overloading the requests to the I/O Server. Estimate how long it takes the I/O Server to read all the data your Citect clients need from the PLCs. If this time is greater or close to the 8 seconds you should increase the LAN timeout parameter until this hardware error message disappears.