The Advanced Modbus driver supports two types of Advanced Modbus channel:
- Advanced Modbus Direct Channel—For controllers that are permanently connected to the ClearSCADA server, for example via a cable, network, or a continuous radio signal.
- Advanced Modbus PSTN Channel—For controllers that communicate with the server using modems.
For the controllers that use direct communications on your system, you need to configure an Advanced Modbus Direct Channel for each uninterrupted communications connection that exists between the ClearSCADA server and Modbus controllers.
For the controllers that use PSTN communications on your system, you need to configure an Advanced Modbus PSTN Channel for each telephone line connection between the ClearSCADA server and the Generic Modbus controllers.
Modbus controllers can communicate with the ClearSCADA server using direct comms or PSTN. With any controllers that communicate using a direct channel but that have a dial-up modem as a ‘backup’ means of contacting the ClearSCADA server, you can configure the controllers to use PSTN as a ‘fallback’ means of communication (see Direct - PSTN Fallback in the ClearSCADA Guide to Advanced Drivers). (In which case, you need to configure a Advanced Modbus PSTN Channel to represent each PSTN line via which the controllers can communicate, in addition to the Advanced Modbus Direct Channel(s).)
In each case, you specify the features for a channel using the fields on the appropriate Advanced Modbus Channel Form.
Each Advanced Modbus Channel Form has several tabs. This section covers configuration of properties that are Advanced Modbus specific. For information on configuring properties that are common to many channels, and for information on tabs not covered in this section, see Tabs on Channel Forms in the ClearSCADA Guide to Advanced Drivers.
Use the fields on the Modbus tab to:
- Specify Whether a Channel Uses Unsolicited PLC Functionality
- Specify the Required Modbus Protocol and Packet Size.
With Direct channels, use the fields within the Scan Groups section of the Scan Parameters tab to specify the frequency with which current data is updated in ClearSCADA (see Define Intervals for Timed Current Data Updates in the ClearSCADA Guide to Advanced Drivers). For ‘Generic’ points (points supported directly by the Advanced Modbus driver, rather than an Extension Driver), the Scan Group interval should be a multiple of the points’ Retrieval Interval rate (see Configure Common Point Properties).