How the X-gateway exchanges I/O Data

Each of the two network interfaces exchange data on it’s network through two buffers. The gateway forwards the data between these buffers as shown below.

 

• Each buffer holds up to 512 bytes of data, which is the theoretical upper limit for the number of bytes that can be exchanged in each direction. However, the actual number of bytes that can be exchanged is highly dependent on the chosen network interfaces.
  
  
• Besides network I/O, these buffers are optionally also used to provide access to network status information, and to control various aspects of the gateway. This may be general diagnostic information (called the ‘Status Word’), list of active slaves (known as the ‘Live List’), or other network specific status information.
  
  
• A dedicated Control Word may be used to start/stop the exchange of data, or to reset the gateway if needed. Most networks distinguish between fast cyclical I/O and less time critical acyclic data. Where applicable, this is also reflected in how data is treated by the gateway and the on-board network interfaces.