General Specifications - Modbus Master/Slave; About The Modbus Protocol - ProSoft Technology CompactLogix MVI69E-MBS User Manual

MVI69E-MBS ♦ CompactLogix™ Platform
Modbus Serial Enhanced Communication Module

8.1.2 General Specifications - Modbus Master/Slave

Communication
Parameters
Modbus Modes
Floating-Point
Data
Modbus Function
Codes Supported
8.2

About the Modbus Protocol

Modbus is a widely-used protocol originally developed by Modicon in 1978. Since that
time, the protocol has been adopted as a standard throughout the automation industry.
The original Modbus specification uses a serial connection to communicate commands
and data between Master and Slave devices on a network. Later enhancements to the
protocol allow communication over other types of networks.
Modbus is a Master/Slave protocol. The Master establishes a connection to the remote
Slave. When the connection is established, the Master sends the Modbus commands to
the Slave. The MVI69E-MBS module can work as a Master and as a Slave.
The MVI69E-MBS module also works as an input/output module between itself and the
Rockwell Automation backplane and CompactLogix or MicroLogix 1500-LRP processor.
The module uses an internal database to pass data and commands between the
processor and Master and Slave devices on Modbus networks.
ProSoft Technology, Inc.
Baud rate: 110 to 115K baud
Stop bits: 1 or 2
Data size: 7 or 8 bits
Parity: None, Even, Odd
RTS timing delays: 0 to 65535 milliseconds
RTU mode (binary) with CRC-16
ASCII mode with LRC error checking
Floating-point data movement supported, including configurable
®
support for Enron, Daniel
1: Read Coil Status
2: Read Input Status
3: Read Holding Registers
4: Read Input Registers
5: Force (Write) Single Coil
6: Preset (Write) Single
Holding Register
8: Diagnostics (Slave Only,
Responds to
Subfunction 00)
, and other implementations
15: Force( Write) Multiple Coils
16: Preset (Write) Multiple
Holding Registers
17: Report Slave ID (Slave Only)
22: Mask Write Holding
Register (Slave Only)
23: Read/Write Holding
Registers (Slave Only)
Reference
User Manual
Page 113 of 159