Specifications

50 Rockwell Automation Publication AG-SG001G-EN-P - April 2015
Chapter 3 Choosing Data Communication Equipment
For Point-to-multipoint (or Broadcast) Half-duplex Applications
Choose full-duplex master radio, half-duplex master radio, or half-duplex remote
radios.
For best performance use a ‘master’ radio modem capable of full-duplex
operation, since a full-duplex radio modem has a transmitter that is separate from
the receiver. This provides shorter RTS-to-CTS delays with each master station
data transmission.
To be cost-efficient, use radio modems that have a transceiver for the remote
stations. Having a transceiver limits modems to only half-duplex operation, since
they can only send or receive data at one time. Therefore, with each remote
station transmission, the RTS-to-CTS delay is longer, since the transceiver takes
time to switch from receiver operation to transmitter operation. This time delay
allows the transmitter time to fully power up.
Also, think about setting up your master station in a redundant configuration. If
the master station's radio modem goes down, the whole communication system is
down. Whereas, when a remote station radio modem goes down, only
communication to a single remote station is lost.
For Multipoint-to-multipoint, Full-duplex Applications
Choose ‘intelligent’ radios. Although ‘intelligent’ radio modems receive and
transmit across the airwaves in a half-duplex fashion, they are able to transfer data
with the attached controller in full-duplex fashion when the controller is
configured to communicate using DF1 radio modem protocol. This allows any
station to trigger a message instruction in ladder logic and immediately transmit
it to the attached radio modem. The radio modem buffers the message and
transmits it once it has an idle channel available.