Modbus TCP / Modbus UDP
vacon • 75
Local contacts: https://www.danfoss.com/en/contact-us/contacts-list/
7
Figure 36. Modbus TCP retransmissions
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
®
AC drive (e.g. Run, Stop, Direction, Speed reference, Fault reset)
•
Access to VACON
®
parameters
•
VACON
®
status monitoring (e.g. Output frequency, Output current, Fault code)
11718_uk
Modbus TCP Communication
PLC
Drive
Modbus
Modbus
TCP
stack
TCP
stack
Modbus Query (1)
Modbus Query (2)
Modbus Query (3)
Modbus Query (4)
Modbus Query
(1,2,3)
Modbus Query (4)
Modbus Response
(1,2,3)
Modbus Response
(4)
TCP Modbus Query
TCP, ACK
TCP, ACK
TCP, ACK
TCP, ACK
TCP, Modbus Response (1,2,3)
TCP, Modbus Response (4)
TCP, Modbus Query (4)
Retransmission
Modbus Query (1,2,3)
Retransmission Modbus Query (1,2,3)
Retransmission
Modbus Query (1,2)
Retransmission
Modbus Query (1)
Modbus
Response (1,2,3)
Modbus
Response (4)
Normal communication continues
P
a
ck
et lost
Summary of Contents for optea
Page 2: ......
