HESG447260R1通用电气卡件
时间服务器。从一个服务器切换到另一个服务器的轮询速率和定时被定义为用户可配置参数。7.4.2步骤将CPU TOD时钟同步到SNTP服务器（使用PME）中定义了这些参数。有关旧系统中的参数定义，请参阅13.3.3附录A：配置高级用户参数。PAC系统™ RX3i和RSTi EP TCP/IP以太网通信用户手册第7节GFK-2224Y 2019年8月SNTP操作128 7.2多SNTP服务器（仅适用于SNTP广播和多播模式）为了防止SNTP定时消息丢失，可以在网络上跟踪多个SNTP时间服务器。以太网接口一次最多可以维护四个SNTP时间服务器的定时信息。每个服务器分配一个决定其优先级的层号。以太网接口使用来自具有最低层号的服务器的消息，直到失去与该服务器的通信。然后，具有下一个最低层号的服务器成为所选择的服务器，并且如果它在150秒内接收到两个定时消息，则以太网接口与它同步。如果定时消息之间的时间间隔超过150秒，则服务器被视为“丢失”。7.3 SNTP定时信号的丢失或缺失如果为SNTP配置了以太网接口，但在150秒内没有从SNTP网络时间服务器接收到两个后续定时消息，则会发生以下情况：▪ 故障条目将放置在PLC故障表中。▪ 故障条目将被放置在以太网接口的异常日志中。可以使用Station Manager读取此日志。▪ 消耗的交换机中的状态字将指示值为3的新数据，而不是正常的1值，表示选择了SNTP，但以太网接口未与SNTP服务器同步。该状态字值可从为特定交换配置的PLC寄存器中获得注意：SNTP错误条件被认为是所有可能的错误代码中最不重要的。因此，如果存在另一个错误条件，其状态代码将出现在状态字中，而不是SNTP错误代码中。一旦失去或缺少同步，以太网接口的内置时钟将按如下方式运行：▪ 如果在上一次通电/重启周期后，以太网接口未收到SNTP服务器的定时消息，则它将继续使用在通电/重新启动时收到的PLC CPU本地时钟值作为其时基。▪ 如果以太网接口已与SNTP服务器同步，但丢失了信号，则将使用最近接收的SNTP时间消息作为其时基。以太网接口将继续向PLC CPU提供时间值以进行时间戳，同时从网络搜索SNTP定时消息。如果稍后收到SNTP消息，则以太网接口将与之同步。PAC系统™ RX3i和RSTi EP TCP/IP以太网通信用户手册第7节GFK-2224Y 2019年8月SNTP操作129 7.4以太网全局数据交换的时间戳CPU为其生成的每个以太网全局数据消息添加时间戳。时间戳指示数据何时从生产PLC的CPU传输到其以太网接口以通过网络传输。时间戳是一个8字节的值，表示自1970年1月1日午夜以来经过的时间。前四个字节包含表示秒的有符号整数，后四个字节包括表示纳秒的有符号整型。
the time servers. Polling rate and timing for switching from one server to another server are defined as user-configurable parameters. These parameters are defined in 7.4.2 Steps to Synchronize the CPU TOD Clock to an SNTP Server (using PME). For parameter definitions in older systems, refer to 13.3.3Appendix A:, Configuring Advanced User Parameters. PACSystems™ RX3i and RSTi-EP TCP/IP Ethernet Communications User Manual Section 7 GFK-2224Y August 2019 SNTP Operation 128 7.2 Multiple SNTP Servers (Applies only to SNTP Broadcast and Multicast Mode) To guard against loss of SNTP timing messages, multiple SNTP timeservers can be tracked on a network. An Ethernet interface can maintain timing information from up to four total SNTP timeservers at a time. Each server assigns a stratum number that determines its priority. The Ethernet interface uses the message from the server with the lowest stratum number until communication with that server is lost. Then the server with the next lowest stratum number becomes the server of choice and the Ethernet interface synchronizes to it if it receives two of its timing messages within a 150-second period. A server is considered "lost" if more than 150 seconds elapse between timing messages. 7.3 Loss or Absence of SNTP Timing Signals If an Ethernet interface is configured for SNTP, but does not receive two subsequent timing messages from an SNTP network timeserver within a 150-second period, the following will happen: ▪ A fault entry will be placed in the PLC Fault Table. ▪ A fault entry will be placed in the Ethernet interface's exception log. This log can be read using the Station Manager. ▪ The Status word within a consumed exchange will indicate new data with a value of 3, instead of the normal 1 value, indicating that SNTP is selected, but the Ethernet interface is not synchronized to an SNTP server. This Status word value can be obtained from the PLC register configured for the specific exchange Note: The SNTP error condition is considered the least important of all possible error codes. Therefore, if another error condition exists, its status code will appear in the Status word instead of the SNTP error code. Upon loss or absence of synchronization, the Ethernet interface’s built-in clock will operate as follows: ▪ If after its last power-up/restart cycle, the Ethernet interface has not received an SNTP server's timing message, it will continue to use the PLC CPU's local clock value that it received at the power-up/restart for its time base. ▪ If the Ethernet interface has been synchronized to an SNTP server but has lost its signal, it will use the most recently received SNTP time message as its time base. The Ethernet interface will continue supplying time values to the PLC CPU for timestamping, while it searches for SNTP timing messages from the network. If SNTP messages are received later, the Ethernet interface will then synchronize to them. PACSystems™ RX3i and RSTi-EP TCP/IP Ethernet Communications User Manual Section 7 GFK-2224Y August 2019 SNTP Operation 129 7.4 Time-Stamping of Ethernet Global Data Exchanges The CPU adds a timestamp to each Ethernet Global Data Message it produces. The timestamp indicates when the data was transferred from the producing PLC's CPU to its Ethernet interface for transmission over the network. The timestamp is an 8-byte value representing the time elapsed since midnight, January 1, 1970. The first four bytes contain a signed integer representing seconds and the next four bytes contain a signed integer representing nanoseconds.
