Modbus Communications - Vacon optea Installation Manual

Modbus TCP / Modbus UDP
PLC
Modbus
Modbus Query (1)
Modbus Query (2)
Modbus Query (3)
Modbus Query (4)
Modbus
Response (1,2,3)
Modbus
Response (4)
Losing one packet is not a big issue because the same request can be sent again after timeout. In
TCP, the packages always reach their destination but if network congestion causes retransmissions,
those packages will most likely contain old data or instructions when they reach their destination.
7.2

Modbus communications

®
The Modbus-VACON interface features are presented below:
• Direct control of VACON
• Access to VACON
®
• VACON status monitoring (e.g. Output frequency, Output current, Fault code)
Local contacts: https://www.danfoss.com/en/contact-us/contacts-list/
Modbus TCP Communication
TCP
stack
TCP Modbus Query
Retransmission
Modbus Query (1)
Retransmission
Modbus Query (1,2)
Retransmission
Modbus Query (1,2,3)
Retransmission Modbus Query (1,2,3)
TCP, ACK
TCP, Modbus Query (4)
TCP, ACK
TCP, Modbus Response (1,2,3)
TCP, ACK
TCP, Modbus Response (4)
TCP, ACK
Normal communication continues
Figure 36. Modbus TCP retransmissions
®
AC drive (e.g. Run, Stop, Direction, Speed reference, Fault reset)
®
parameters
vacon • 75
Drive
TCP
Modbus
stack
Modbus Query
(1,2,3)
Modbus Response
(1,2,3)
Modbus Query (4)
Modbus Response
(4)
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