User manual

IEC61131 User and Reference Manual
April 22, 2008
73
Figure 24: Modbus RTU Configuration (Advanced) Dialog Box
The Message Size grouping parameters are used to control the message size for the
protocol. Control over message length is needed when writing large amounts of data over
certain communication networks. A larger value can improve communication speed but can
increase the number of failed transmissions. A smaller value can reduce the number of failed
transmissions but may reduce throughput.
The Maximum selection indicates that the host application is to package messages using
the maximum size allowable by the protocol.
The Custom Value selection specifies a custom value for the message size. This value
indicates to the host application to package messages to be no larger than what is specified,
if it is possible. Valid values are 2 to 250 when Addressing is set to Extended and Station is
255 or higher. When Addressing is set to Extended and Station is less than 255 valid values
are 2 to 252. When Addressing is set to Standard valid values are 2 to 252.
 Click Restore Defaults to restore default values to all fields on this page.
Information
Information displays detailed driver information. When the Information tab heading is clicked
the Information dialog is opened as shown below.