Introduction of the SNTP ProtocolΒΆ
The Protocol SNTP (Simple Network Time Protocol) provides the functionality to synchronize the clock of a PLC to an external time source. For further information and specification of the protocol please refer to the document RFC4330.
The following modes are supported by the implementation of the AC500 PLC:
- SNTP Client
- SNTP Server
- SNTP Client and Server
The Function Block PmSntpInfo can be used to read diagnosis information of the protocol.
Refer to the documentation of the library ABB_Pm_AC500.lib for further information.
Note
- If a high precision of system time is wanted, use a fully functional NTP server or at least a SNTP server with a high-precision time-source (e.g. DCF-77 receiver). Avoid cascading several levels of SNTP server / SNTP clients.
- Client requests are normally sent at intervals depending on the frequency tolerance of the client clock and the required accuracy. However, under no conditions requests should be sent at less than one minute intervals (see RFC 4330). Keep that in mind when setting polling-interval of the SNTP client, especially if a huge amount of clients use one single server.
- Be sure not to use broadcast or multicast addresses as server or backup-server since current SNTP implementation does not support manycast mode.