Banner SureCross DX80 Series Manual page 13

SureCross™ FlexPower™ Data Radio
Serial radios connect a Modbus control system to one or more DX80 Gateway devices acting as Modbus slaves. The data radios do not use
addressing, error checking, or acknowledgement in the radio packets. Instead, the data stream appearing on the serial input of one radio within
the network is reproduced on the serial outputs of all other radios in the same network. Addressing and error correction occur at the application
layer. The system operates as it would in a hardwired Modbus multi-drop serial network, except with an increased latency, as described in the
Timing section.
All deterministic properties of the DX80 I/O networks are preserved. If a data radio link drops multiple packets, the target DX80 Gateway reacts
as if the serial line was cut, driving all outputs in the local TDMA system to the predefined state. The data radio links are collision free because
the master control system uses polling to initiate all data exchanges so all data radio packets originate from the same place.
Each DX80 I/O network is inherently collision free. The only potential collisions on the two radio links occur when hardwired DX80 Gateway
devices and data radios are collocated. Fortunately, the application layer (Modbus) retries the packet until it succeeds. Using 2.4 GHz radios
for the DX80 I/O network links and 900 MHz in the data radio links (or vice versa) also minimizes data collisions.
Within any data radio network, there are two types of device: masters and slaves. Every network needs one master and the remainder of the
devices are slaves. Use the data radio's right rotary switch to determine which device is the master and which devices are the slaves. Set
the right rotary switch to 0 to select the master function and select 1 for the slaves. The master/slave settings establish which device is the
timekeeper for the network.
Note that the master/slave function of the data radio network is at the physical layer; it has no bearing on the Modbus functionality at higher
network layers, e.g. the Modbus master need not be wired to the data radio master.
Gateway
NID 1
Node
NID 1
The Modbus master inside the PC connects serially to the data radio on Network ID (NID) A. Two data radio slaves programmed to NID A
communicate with the data radio master. Each data radio slave is hard-wired serially to a DX80 Gateway, communicating using the Modbus protocol.
Each DX80 Gateway, in turn, is using a wireless I/O link to communicate with two DX80 Nodes. All three wireless networks shown can coexist
because they are on unique network IDs.
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P/N 132031 rev. E
Network Implementation Details
Modbus Master
Host System
(e.g. Modbus Master)
Data Radio
NID A
Node
NID 1
Data Radio
NID A
Gateway
Data Radio
NID 2
NID A
Node
NID 2
Banner Engineering Corp. • Minneapolis, MN U.S.A
www.bannerengineering.com • Tel: 763.544.3164
Node
NID 2