MiniCapt Remote Microbial Air Sampler Operations Manual
Page 5-1
Chapter 5
Modbus Protocol
Communications with the MiniCapt Remote Microbial Air Sampler 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 contains three 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:
The supported functions include:
1
Read Coils
3
Read Holding Registers
4
Read Input Registers
5
Write Single Coil
6
Write Single Holding Register
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.
