Command/response mode – Comtrol Modbus TCP User Guide User Manual
Page 22
22 - Chapter 2. Programming Interface
DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I
Command/Response Mode
2.2.4.2. Command/Response Mode
The Command/Response mode provides the following functionality:
•
A synchronous transfer mode for sending and returning responses from all Modbus and Application
Ethernet TCP/IP interfaces to serial and Ethernet TCP/IP devices.
•
Only one command message is transmitted at a time. Command messages are queued if a command
message is active.
•
Responses are routed only to the message sender.
•
Responses are timed out and old responses, (ones not requested within a certain time frame), destined for
the Modbus interface are discarded.
•
The expected response count is configurable. While this is typically one, some devices may return multiple
responses per message.
The Command/Response transfer mode is typically required in installations that require multiple controllers
sending raw/ASCII messages with expected responses, and it is desired that each controller only receive its
own responses.