System behavior

TwinCAT handles the redundancy case in real-time, and the user has no intervention option. However, information on the current status is provided by variables in the System Manager.

• SlaveCount/SlaveCount2
  This indicates how many EtherCAT slaves are at present being reached through the primary or redundancy port. This information refers to the most recent cycle.
• FrmXWcState
  This information refers to the most recent cycle. It is recommended that this accumulated information for all the working counters of an EtherCAT frame is monitored on the application level, even in redundancy mode.
• DevState
  The meanings of the bits
• 0x0001: Link error at primary port
• 0x0004: Link error at redundancy port
• 0x0008: Missing one frame
• refer to the cable redundancy. If all three bits are zero, then the status of the cable redundancy is normal, and the next connection fault can occur.
  Under some circumstances the link status messages can be delayed by a few milliseconds. They can therefore not be used in a real-time context.

The redundancy case is illustrated accordingly in the Topology display.

• Fig. Typical error patterns in the redundancy case, top: Interruption at redundancy port
• Fig. Typical error patterns in the redundancy case, center: 2 interruptions, communication failure to one terminal block.
• Fig. Typical error patterns in the redundancy case, bottom: Terminal in the second terminal block removed while running, causing interruption in power supply to subsequent terminals and failure of communication with them.

The redundancy case Redundancy is an irregular operating condition. It is recommended that occurrence of the redundancy case is detected at an early stage through evaluation of the diagnostic variables shown above, and that the cause is rectified promptly.