MODBUS Protocol
Serial Communication Parameters
C-2
Model 49
i
Instruction Manual
Thermo Fisher Scientific
Serial Communication
Parameters
The following are the communication parameters that are used to configure
the serial port of the
i
Series to support MODBUS RTU protocol.
Number of Data bits : 8
Number of Stop bits
: 1
Parity :
None
Data rate
: from 1200-115200 Baud (9600 is default)
TCP Communication
Parameters
iSeries Instruments support the MODBUS/TCP protocol. The register
definition is the same as for the serial interface.
TCP connection port for MODBUS : 502
Application Data Unit
Definition
Here are the MODBUS ADU (Application Data Unit) formats over serial
and TCP/IP:
Slave Address
The MODBUS slave address is a single byte in length. This is the same as
the instrument ID used for C-Link commands and can be between 1 and
127 decimal (i.e. 0x01 hex to 0x7F hex). This address is only used for
MODBUS RTU over serial connections.
Note
Device ID ‘0’ used for broadcast MODBUS commands, is not
supported. Device IDs 128 through 247 (i.e. 0x80 hex to 0xF7 hex) are not
supported because of limitations imposed by C-Link.
MBAP Header
In MODBUS over TCP/IP, a MODBUS Application Protocol Header
(MBAP) is used to identify the message. This header consists of the
following components:
Serial:
Slave Address
Function Code
Data
Error Check
TCP/IP:
MBAP Header
Function Code
Data
Transaction Identifier
2 Bytes
0x0000 to 0xFFFF (Passed back in response)
Protocol Identifier
2 Bytes
0x00 (MODBUS protocol)
Length
2 Bytes
0x0000 to 0xFFFF (Number of following bytes)
Unit Identifier
1 Byte
0x00 to 0xFF (Passed back in response)
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