Banner SureCross DX80 Wireless Networks - Manual (Page 6)

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P/N 136689
Banner Engineering Corp. • Minneapolis, MN U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
DX80
Reference Guide
Network Basics
Modbus RS-485
Modbus Remote Terminal Unit (RTU) running over RS-485 cabling is sometimes abbreviated as Modbus 485 and is a master-slave
communications protocol typically used for industrial applications . RS-485 refers to the physical layer of the network .
Modbus 485 is used for the hard-wired interface on Banner’s SureCross™ wireless products . The particular variation of RS-485 chosen
for Banner’s SureCross wired network is 2-wire RS-485 running at 19 .2 kilobits per second (kbps) .
All connections between a DX83 Ethernet Bridge and a DX80 Gateway are via Modbus 485, as are connections between DX80 devices
and the DX85 Expanded Remote I/O modules . A basic DX80 Gateway can be connected to a PLC or other process controller using the
Modbus 485 network .
One Modbus master and up to 247 slave nodes may be connected to the bus at any given time, with the slave devices assigned unique
slave identification numbers .
Only the Modbus master is allowed to initiate communications on a Modbus network . Messages from the master indicate for which slave
device a message is intended and only the slave addressed by the master is allowed to respond . This allows the Modbus protocol to
work well with a physical “party line,” where everyone “hears” all the network traffic, but only the addressed slave device can respond.
In a traditional Modbus network, the slave devices cannot alert the master when an event occurs. Instead the master must continually
poll each slave device to observe changes .
SureCross and Modbus
Specific to Banner’s SureCross network, all standard Gateways ship from the factory configured as Modbus slaves with their Modbus
slave ID number set to 1. To avoid communications problems, do not connect the SureCross Gateway to a Modbus network already
containing a slave ID 1 device .
As shown, the DX80 Gateway is a slave device within the Modbus network but remains the master device of the wireless network. In
this way, the DX80 Gateway behaves as a true networking gateway by bridging communications between the wireless network and the
Modbus RTU network .
The Modbus register map of the Gateway is fixed; there is no setup, programming, or customization needed to use Modbus to access
the I/O points on wireless network device .
When a new Node is powered up and added to the wireless network, the Modbus registers are activated at a unique location saved for
each wireless network Node device. Refer to Banner’s Modbus User’s Guide, document part number 132114, for more information about
the Modbus register map .
Network 1: Gateway as Modbus Slave
Wireless Network
Device 1
Device 2
Wireless Master
Device (Device 0)
Modbus Network
Modbus Master Device
Slave ID 2
Slave ID 3
Slave ID 1
RS 485
Cable