Hardware reference guide

Network Configurations
50
35013379 02 October 2007
Quantum Modbus and Modbus Plus Communications
Overview Each Quantum CPU includes both a Modbus and Modbus Plus communications
port. The features offered by both these communication protocols are listed in the
following table.
Modbus and
Modbus Plus
Features
The following table shows the Modbus and Modbus Plus features.
Modbus Modbus, a master/slave protocol, is a de facto industry standard with support from
over 500 industrial suppliers.
On-line programming or data acquisition applications are easily supported directly
from the serial port of any computer.
Modbus can be used in either a simple point-to-point manner with a pair of devices,
or in a network architecture with up to 247 slave devices.
Modbus Plus Modbus Plus combines high speed, peer-to-peer communication and easy
installation to simplify applications and reduce installation costs.
It allows host computers, controllers and other data sources to communicate as
peers throughout the network via low-cost twisted pair cable or optional fiber optic
cable.
As a deterministic token-passing network, Modbus Plus communicates at one
megabaud for fast access to process data. It’s strength is its ability to control real-
time control devices like I/O and drives, without degraded performance due to
loading or traffic.
Features Modbus Modbus Plus
Technique Slaves polled by a master Peer-to-peer, token rotation
Speed 19.2K typical 1 M
Electrical RS-232, various others RS-485
Distance without repeater RS-232, 50 ft. (15 m) 1,500 ft. (457 m)
Media Various Twisted pair, Fiber optics
Max nodes per network 247 64
Max network traffic 300 registers/sec @ 9.6 Kb 20,000 registers/sec
Programming Yes Yes
Read/Write data Yes Yes
Global data No Yes
Peer Cop No Yes
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com