LiQuilaz II E and S Operations Manual
Page C-1
Appendix C
Modbus TCP Protocol
Communications with the LiQuilaz II particle counter are available via Modbus TCP. The
instrument presents a single TCP/IP Ethernet connection at port 502 using the
standard Modbus protocol.
Two specification documents were used in the development of the Modbus interface:
• “MODBUS MESSAGING ON TCP/IP IMPLEMENTATION GUIDE V1.0b”
• “MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1b”
The Modbus protocol, as implemented in this instrument, utilizes generic 0-based
addressing.
Modbus Overview
Each register in the Modbus map is defined to be 16 bits. The map can contain three
distinct sections:
1
Input registers
Read Only information for ID and data collection
2
Holding registers
Read/Write parameters for configuring the device
3
Coils
Read/Write individual bits to control the device
The supported functions include:
1
Read Coils
3
Read Holding Registers
4
Read Input Registers
5
Write Single Coil
6
Write Single Holding Register
15
Write Multiple Coils
16
Write Multiple Holding Registers
22
Mask Write Holding Register
23
Read/Write Multiple Holding Registers
• Any registers accessed but not defined will generate an address error.
• Spare coils/registers will “set” without error and always return a zero value.
• Registers set with invalid data will return a function error.
