EtherCAT Servo State and Monitoring

Developing IgH Applications

6.6 CiA 402 Servo State Machine

Many EtherCAT servo drives use the CoE CiA 402 state machine. A common control sequence is:

Fault Reset
    ↓
Shutdown (0x0006)
    ↓
Switch On (0x0007)
    ↓
Enable Operation (0x000F)
    ↓
Write target position / velocity / torque

Actual control-word decisions must use the status-word mask and the drive manual. Requirements for PDOs, units, enable sequences, and stopping behavior may differ between operating modes.

6.7 State Monitoring

The application should check the following states periodically or when events occur:

• ec_master_state_t: Master link, number of slaves, and AL state.
• ec_domain_state_t: Domain working counter and working counter state.
• ec_slave_config_state_t: Whether the slave is online and operational.
• Slave status word, error code, and vendor-specific diagnostic objects.

An incomplete working counter generally indicates that a slave is offline, the PDO configurations do not match, or some datagrams did not receive responses. Do not continue outputting hazardous control values while the working counter is abnormal.