Use these fields on the Modbus tab to specify the type of Modbus protocol that the channel is to use and the maximum size of the data packets that can be transmitted via the channel:
- Protocol Type—Use this field to specify the type of Modbus protocol that the channel is to use. Choose RTU, ASCII, or TCP, as required (the TCP option only applies to Network channels).
- Maximum Packet Size—Messages are transmitted as blocks of data known as packets. With the Modbus protocol, each data packet has to contain a complete message.
Use the spin box to specify the maximum acceptable packet (message) size of:
- Requests that ClearSCADA can send to a controller on this channel
- Replies that a controller on this channel can send to ClearSCADA. (The size that you define excludes framing and checksum bytes.)
Should ClearSCADA or a controller need to send more information than can be contained within one message, it will send further message(s) containing the data that had to be omitted from the original message.