GW-2139M (Modbus TCP to BACnet MS/TP Gateway) User Manual
Version 1.0.0
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1. General Information
1.1 BACnet MS/TP Introduction
BACnet is a data communications protocol for Building Automation and Control Networks.
BACnet Master Slave Token Passing (MS/TP) protocol is used to relay and exchange
information between building devices. BACnet MS/TP is a based on BACnet standard protocol
SSPC-135, Clause 9. BACnet MS/TP is a peer-to-peer, multiple master protocol based on token
passing. A token is information packets in the form of a pulse signal that is passed between
devices on a network. BACnet MS/TP is exclusive to BACnet and can be implemented using the
EIA-485 signaling standard. This is a shielded twisted-pair (STP) LAN operating at speeds from
9600 bit/s to 76800 Kbit/s. This LAN type is particularly suitable for single controller and low cost
communications.
1.2 Modbus TCP Introduction
MODBUS/TCP is a variant of the MODBUS family of simple, vendor-neutral communication
protocols intended for supervision and control of automation equipment. Specifically, it covers the
use of MODBUS messaging in an “Intranet” or “Internet” environment using the TCP/IP protocols.
The most common use of the protocols at this time are for Ethernet attachment of PLC’s, I/O
modules, and gateways to other simple field buses or I/O networks.
