The Modbus time synchronization can be done in several ways. Over the serial interface, the host's synchronization write can be given with the Modbus broadcast address "0". Thus, all protection relays in the same serial network can be synchronized at the same time.
Method 1: Synchronization in one step
Registers 49201...49208 (49211...49218) should be written in one multiple registers preset request (function 16) by a Modbus TCP/IP client or by a serial interface client. The protection relay's Modbus address or the Modbus broadcast address can be used with the serial interface. If the clock is written in one step, the write value of the register 49201 (49211) is not checked by the protection relay.
Method 2: Synchronization in three steps
- The client reserves the time synchronization by writing value "1" to the register 49201 (49211). If necessary, check that the reservation value is zero at the beginning. If the time synchronization writing is already reserved by another client, the protection relay returns the exception response 03.
- The client writes the time structure to the protection relay. This can be done in one transaction or alternatively each register can be written separately.
- The client sets the clock by writing "2" into the register 49201 (49211). When the value "2" is written, the timesync registers are latched onto the protection relay's internal clock and the reservation in 49201 (49211) is released.
There is an internal timeout for the clock setting. The time synchronization reservation is released if the clock is not set within two minutes. The client can abort the time synchronization at any time by writing "0" into the register 49201 (49211). In that case the real-time clock is not set at all.
Other Modbus clients can read the currently running real-time clock even if the time writing is reserved by another client.