Description
3.2 Modbus TCP functions
SIRIUS 3RW5 Modbus TCP communication module
22 Manual, 03/2018, A5E43676481002A/RS-AA/001
Connection monitoring function - "TCP keep-alive monitoring"
To avoid blocking the communication link permanently if the communication partner fails,
Modbus TCP provides the "TCP keep-alive monitoring" function for monitoring the
connection.
The following parameters can be permanently set for this purpose:
● Keep-alive time: 300 s
● Keep-alive maximum attempts: 1
● Keep-alive interval: 75 s
If no TCP data transmission is detected within 375 seconds, the "TCP keep-alive monitoring"
function signals connection broken and ends the communication link automatically. On a
broken connection, the 3RW5 soft starter responds as set in parameter "Response to
CPU/Master Stop" (Page 45).
Connection monitoring function - Access monitoring of the control source
An independent connection monitoring function monitors the write access of the authorized
Modbus client within the access monitoring time. Only the Modbus client, which is the first to
set up a communication link to the server, is authorized for this access.
A write access of the Modbus client to the server (process image outputs (PIQ), parameter)
must be repeated regularly. If the write process is not repeated for the duration of the access
monitoring time, the 3RW5 soft starter interprets this condition as a broken connection to the
Modbus client. The 3RW5 soft starter responds as set in the parameter "Response to
CPU/Master Stop" (Page 45).
You will find the "Access monitoring time" parameter in the data table "Communication
parameters" (Page 99). The factory setting is 5 seconds.
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