SERVO_OFFSET is a system parameter that is usually set by the operating system.  The value depends on the SERVO_PERIOD, the modules fitted (to a MC664X) and the model of Motion Coordinator.  It should not be necessary to set this in a system.  Only change the value if told to by Trio's engineers.  Incorrect setting may cause non-starting of EtherCAT and missed encoder counts in analogue systems.

Tip: SERVO_OFFSET is sometimes confused with the EtherCAT SYNC0 offset.  These are 2 very different settings.  Sync0 is a feature of the EtherCAT slave device that is set up by the master.  Sync0 is set globally by the ETHERCAT function $91 or for individual slaves by NODE_SYNC_OFFSET.