User manual

IEC61131 User and Reference Manual

April 22, 2008

The Addressing parameter selects standard or extended Modbus addressing. Standard

addressing allows 255 stations and is compatible with standard Modbus devices. Extended

addressing allows 65534 stations, with stations 1 to 254 compatible with standard Modbus

devices. The default is Standard.

The Station parameter sets the target station number. The valid range is 1 to 255 if standard

addressing is used, and 1 to 65534 if extended addressing is used. The default is 1.

The Timeout parameter sets the length of time, in seconds, to wait for a response from the

controller before retrying (see Attempts), or ultimately failing. Valid entries are 1 to 255. The

default is 3.

The Attempts parameter sets number of times to send a command to the controller before

giving up and reporting this failure to the host application. Valid entries are 1 to 20. The

default is 3.

This Serial Port Settings grouping contains details directly related to the PC‟s

communication port including the port number, the baud rate, parity and stop bit settings.

The Port parameter specifies the PC serial port to use. The DNP driver determines what

serial ports are available on the PC and presents these in the drop-down menu list. The

available serial ports list will include any USB to serial converters used on the PC. The

default value is the first existing port found by the driver.

The Baud parameter specifies the baud rate to use for communication. The menu list

displays selections for 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, and 57600. The

default value is 9600.

The Parity parameter specifies the type of parity to use for communication. The menu list

displays selections for none, odd and even parity. The default value is None.

The Data Bits parameter specifies the number of data bits contained in the character frame.

Valid values are for this field is 7 and 8 bits. The default value is 8 bits.

The Stop Bits parameter specifies the number of stop bits to use for communication. The

menu list displays selections for 1 and 2 stop bits. The default value is 1 bit.

The Connection Type parameter specifies the serial connection type. The Modbus ASCII

driver supports direct serial connection with no flow control, Request-to-send (RTS) and

clear-to-send (CTS) flow control and PSTN dial-up connections. The menu list displays

selections for Direct Connection, RTS/CTS Flow Control and Dial Up Connection. The

default selection is Direct Connection.

 Select Direct Connection for RS-232 for RS-485 connections that do not require the

hardware control lines on the serial ports.

 Select RTS/CTS Flow Control to communicate over radio or leased-line networks

using modems that require RTS/CTS handshaking. Selecting RTS/CTS Flow Control

adds a new tab, Flow Control, to the Modbus ASCII Configuration dialog. Refer to the

Flow Control Parameters section below for configuration details.

 Select Dial Up Connection to communication over dial up modems. Selecting Dial Up

Connection adds a new tab, Dial Up, to the Modbus ASCII Configuration dialog. Refer

to the Dial Up Parameters section below for configuration details.

 Click Restore Defaults to restore default values to all fields on this page.

Modbus ASCII Configuration (Flow Control)

Flow Control parameters are used to configure how RTS and CTS control is used. When

RTS/CTS Flow Control is selected for Connection Type the Flow Control tab is added to the