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MODBUS communication
The following chapter contains:
● General information on MODBUS
● MODBUS RTU protocol
● MODBUS ASCII protocol
● MODBUS functions
● Data library
10.1
General information on MODBUS
The ATC6500 supports the MODBUS RTU, MODBUS TCP and MODBUS ASCII protocols
via the following interfaces:
● Integrated RS485 interface on the device
● Expansion module Ethernet (3KC9000-8TL75)
Via these two interfaces it is possible to modify the status of the ATC6500, as well as of the
parameters using third-party supervision software (scada) or by means of other devices such
as PLCs. The communication via MODBUS TCP is only possible via the Ethernet expansion
module (3KC9000-8TL75).
Setting the communication parameters
The parameters can be set by means of the P10 - Communications (Page 177) menu.
10.2
MODBUS RTU protocol
If the MODBUS RTU protocol is used, the following structure must be observed:
T1
Address
T2
(8 bit)
T3
Address: Contains the serial address of the slave target device.
Function: Contains the code of the function that is performed by the slave.
Data: Contains the data that is sent to the slave, or the data of a query received by the slave
(maximum length 80, 16-bit register).
CRC: This is used for an integrity check. If a message is corrupted by electric noise or
interference, the CRC field enables the ATC6500 to detect the error and thus ignore the
message.
3KC ATC6500 transfer control device
Manual, 05/2019, L1V30538268002A-01
Function
Data
(8 bit)
(N x 8 bit)
CRC
T1
(16 bit)
T2
T3
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