The Modicon Modbus Protocol Reference Guide PI-MBUS-300 provides the
detailed protocol information needed to interpret the messages. The Modbus
protocol specification is also available on the world wide web at:
http://www.modicon.com/techpubs/toc7.html
4-3. LC/Modbus Operation and Diagnostics
U3-1050 4-6 11/98
Westinghouse Proprietary Class 2C
4-3.4. Interpreting the Ovation Link Controller Module LEDs
The row of LEDs on the face of the LC electronics module displays information
about the operation of the interface. These LEDs are labeled 1 through 8 on the
module case. The meaning of each LED is shown in Table 4-3:
As can be seen in the table, the first of the eight indicator LEDs, called LED 1,
indicates that a message is being sent. LED 2 indicates that the software has begun
to wait for message reception. When a message has been received, the LED is
extinguished. If no message is received, the LED will be extinguished after the
timeout period has expired.
During normal operation, LED 1 and LED 2 are seen to alternate rapidly. If LED 1
appears to be on for a very short time and LED 2is on for a long time or appears to
be on all the time, this usually 

Modicon Modbus协议参考指南PI-MBUS-300提供了
解释消息所需的详细协议信息。Modbus协议
协议规范也可在万维网上获取，网址为：
http://www.modicon.com/techpubs/toc7.html
4-3. LC/Modbus操作和诊断
U3-1050 4-6 11/98
西屋专有2C级
4-3.4. 解读Ovation链路控制器模块LED
LC电子模块正面的一排LED显示信息
关于界面的操作。这些LED在屏幕上标记为1到8
模块外壳。每个LED的含义如表4-3所示：
从表中可以看出，八个指示灯LED中的一个被称为LED 1，
指示正在发送消息。LED 2表示软件已启动
等待消息接收。当收到信息时，指示灯点亮
熄灭。如果未收到任何信息，则LED将在发送后熄灭
超时时间已过期。
在正常工作期间，LED 1和LED 2快速交替。如果LED 1
LED 2亮起时间很短，LED 2亮起时间很长或
一直开着，通常是这样