Endress+Hauser Liquiline CM44 series - Tcp; Rtu

SD01189C/07/EN/04.17
Endress+Hauser
8 © Copyright Dec. 2016
3.3.2 RTU
The data are transmitted in binary format and are therefore more compact.
Address
Function
Data
CRC16
1 character
1 characters
N character
2 characters
0 = Broadcast
247 = Unicast
A delimiter of at least 3.5 characters must be maintained between two Modbus telegrams.
Field
Length
Info
Client
Server
Address
1 Byte
Identifies target
Set by the client
Copied from the
request into the
reply
CRC16
2 Byte
 Modbus specification
Set by the client
Set by the server
3.3.3 TCP
As with RTU, the data are transmitted in binary format. Address and checksum used in RTU mode are
dispensed with. The Modbus ADU is embedded in the TCP/IP telegram.
Modbus TCP/IP ADU
MBAP header
Modbus PDU
Transaction
number
Protocol
attribute
Number of
bytes
to follow
Address
Function
Data
2 Byte
2 Bytes
2 Bytes
1 Byte
1 Byte
N Bytes
= 0x0000
= N + 2
= 0
Field
Length
Info
Client
Server
Transaction
number
2 Byte
Identifies the transaction
Set by the client
Copied from the
request into the
reply
Protocol attribute
2 Byte
Set by the client
Copied from the
request into the
reply
Number of bytes to
follow
2 Byte
Number of bytes to follow
Set by the client
Set by the server
Address
1 Byte
Identifies a slave that is
connected to a serial bus
located downstream.
Note
The devices in the Liquiline
product family do not use the
unit identifier. This should
always be set to 0.
Set by the client
Copied from the
request into the
reply
Via the TCP port 502, you can use up to 3 parallel TCP connections with the device simultaneously.
Please note the correct structure of the MBAP header.