Applies To:
  • CitectSCADA 5.xx

Summary:
The Mitsubishi serial protocol uses 'Station number', 'PC number' and 'Message wait time' fields. What functionality do these fields provide, and how does Citect's MELSEC driver support this functionality? 

Solution:
The 'Station Number', 'PC Number' and 'Message wait time' can be set by using the address field in the IODevices form as follows:

IO Devices form

Protocol: MELSEC or MELSEC1

Address: stationno[,pcno[,waittime]]

where:

[ ] indicates an optional setting.

stationno = Station Number
The station number is used in a RS422/RS485 multidrop configuration to identify each station. On the Computer Link Module (AJ71) this station number is set by two rotary switches. In a point to point connection (PC-PLC) the station number is commonly set to 00, but every other setting is possible, as long as the number set by the rotary switches is equal to the number set in Citect. The Station Number specified in the Citect forms is represented in decimal, and the valid range is 00 to 31. This setting is NOT optional.

pcno = PC CPU number
The PC CPU number is used to access a specific PLC CPU in the MELSEC NET. So, if the Computer Link Module is placed in the master of the MELSEC NET, then every local station in the MELSEC NET can be reached by setting the corresponding PC CPU number. If communication is needed with the PLC CPU where the Computer Link Module is placed, the number 255 (indicating host or 'self') has to be set. This PC CPU number specified in the Citect forms is represented in decimal, and the valid range is 00 to 64 and 255. This setting is optional, and the default is 255.

waittime = Message wait time
This is a time delay required for some computers to switch from send to receive states. The message wait time determines the minimum waiting time before the Computer Link Module sends data after receiving it from the computer. This is useful when simple RS232/RS485 converters are used. This Message Wait Time specified in the Citect forms is represented in decimal, and the valid range is 0 to 15 (representing a delay of 0 to 150msec). This setting is optional, and the default is 0.


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