SYNC protocol
The SYNC protocol provides the basic network synchronization mechanism. The SYNC producer triggers the synchronization object (SYNC) periodically. The transmission period of this SYNC protocol is configurable. Any CANopen FD device can be configured as SYNC consumer. The purpose for which the SYNC protocol is used, is manufacturer-specific. In many cases, the SYNC protocol is used for busload management purposes. In such use cases, TPDOs in the SYNC consumers are triggered by the reception of a pre-configured number of SYNCs. To establish an explicit relationship between the current SYNC cycle and PDO transmissions, the SYNC start value (sub-index 06h in the TPDO communication parameters) is used. The current SYNC cycle is provided in the one-byte SYNC counter value.
The SYNC counter is incremented by 1 with every SYNC transmission. The initial value of the counter is 1. The maximum value is configurable in the data object synchronous counter overflow 1019h. In case the maximum value is reached the SYNC counter is set to 1 with the next transmission. The value of the counter is reset to 1 if the CANopen FD device leaves the NMT state stopped.