Applies To:
  • CitectSCADA 5.20

Currently the MODNET driver has been designed to communicate over TCPIP in a point-to-point fashion. This implies that each PLC has a dedicated IP address, and hence each port supports only one unit. In this manner, the actual unit address is not relevant. The protocol used by the MODNET driver expects the address field in the protocol frame (termed DEST_ID) to be set to zero.

As a gateway is now available that can be used to communicate with multiple units, the driver needs to be enhanced to also support a multi-drop architecture. In this new configuration, the IP address defined for a port is the IP address of the gateway, and the units attached to the gateway are defined in their own devices form (linked to the gateway ports form). The units attached to the gateway will have their unit address defined in the device form. The gateway expects the address field in the protocol frame (termed DEST_ID) to be set to the unit address of the device the gateway is to communicate with.


The driver, version 2.xx.xx.xxxx determines if it is multidrop connection or point-to-point connection parsing the parameter string in an "Address/IODevice" form.

Blank address field indicates that it is point-to-point connetion.

The Citect.ini file parameter "MaxOutstanding" is now to be placed under the section [MODNET.<Port_name>]

being Port dependent. Each open port may have it's own parameter.


MaxOutstanding =3 for port TCPPORT1

MaxOutstanding =4 for port TCPPORT2