A synchronization (SYNC) object provides synchronous communication on a CANopen network. An SYNC producer broadcasts SYNC messages in the network periodically. An SYNC message is a single CAN frame with an identifier 128 (080h) by default. You can configure devices to transmit synchronous PDOs when these devices receive an SYNC message. Each device may have a time jitter in transmission when other objects have higher priority identifiers or transmitting orders. The maximum time jitter indicates the quality of the synchronization.

The time period between SYNC messages depends on the communication cycle period parameter. You may configure this parameter during the boot-up process. Synchronous Counter Overflow

The synchronous counter overflow object is an object dictionary entry that defines the maximum value of the SYNC counter. The SYNC counter is an optional part of an SYNC message. You can enable the SYNC counter by specifying a non-zero value to the synchronous counter overflow object.

The SYNC counter value starts from 1 and increases by 1 with each SYNC message. An SYNC cycle is the time period between the time when the SYNC counter value is 1 and the time when the SYNC counter value reaches the synchronous counter overflow value. At the end of an SYNC cycle, the device sends out the SYNC message with a counter value that equals the synchronous counter overflow value. The device then resets the SYNC counter value to 1 for the next SYNC message. The next SYNC message starts another SYNC cycle.

Use the synchronous counter overflow object to ensure periodic SYNC events occur in SYNC cycles with the same SYNC counter value. You can use specific SYNC counter values to trigger multiple periodic SYNC events. For example, you can set the periods of event A and event B to 3 and the period of event C to 4. You then set the synchronous counter overflow to 12. When you execute the application, event A and event B occur when the SYNC counter is 3, 6, 9, and 12. Event C occurs when the SYNC counter is 4, 8, and 12.

Table 5. Values Supported by the Synchronization (SYNC) Object
Value Description
0 The SYNC message is a CAN message containing 0 data bytes. The SYNC message does not contain an SYNC counter.
1 Reserved.
2 to 240 The SYNC message is a CAN message containing 1 data byte. The data byte is an SYNC counter.
241 to 255 Reserved.