User manual

IEC61131 User and Reference Manual
April 22, 2008
60
Modbus ASCII in TCP
Modbus ASCII in TCP message format is exactly same as that of the Modbus ASCII
protocol. The main difference is that Modbus ASCII in TCP protocol communicates with a
SCADAPack controller through the Internet and Modbus ASCII through the serial port. The
Modbus ASCII in TCP protocol does not include a six-byte header prefix, as with the
Modbus\TCP, but does include the Modbus „CRC-16‟ or „LRC‟ check fields.
 To configure a Modbus ASCII in TCP protocol connection, highlight Modbus ASCII in
TCP in the Communication Protocols window and click the Configure button. The
Modbus ASCII in TCP Configuration window is displayed.
 To select a configured Modbus ASCII in TCP protocol connection, highlight Modbus
ASCII in TCP in the Communication Protocols window and click the OK button.
 To close the dialog, without making a selection click the Cancel button.
General Parameters
When Modbus ASCII in TCP is selected for configuration the Modbus ASCII in TCP
Configuration dialog is opened with the General tab selected as shown below.
Figure 15: Modbus ASCII in TCP Configuration (General) Dialog Box
The Modbus Communication Settings grouping contains Modbus specific communication
settings including the addressing mode, the station address, the timeout interval as well as
the number of attempts.