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This error means that the current I/O data could not be passed to the firmware.

I/O Data transfer to the firmware/device is initiated by so-called handshake flags that synchronize the access to the data areas. There are several access rules, when the host is allowed to access the I/O areas. A firmware needs some time to copy the data from the dual-port memory to the internal buffers and during this time the area is locked for the host.

In this state the driver has the possibility to wait, if a timeout is passed to the function, for the area being released by the firmware. If no timeout is passed the error CIFX_DEV_EXCHANGE_FAILED is returned.


The most common causes are:

  • Delay between two consecutive calls to xChannelIORead/xChannelIOWrite with timeout=0 is too short for the fieldbus device to copy the data from the DPM
  • Wrong usage of PLC functions (e.g. Calling xChannelPLCActivateRead while xChannelPLCIsReadReady returns false)
  • If a timeout is passed and the cifX Toolkit is used, it might be an error in the implementation of OS_GetMillisecondCounter() as this results in a wait time that is too short