Allen-Bradley 1756-L63XT, User Manual

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Rockwell Automation Publication 1756-UM001O-EN-P - October 2014 107
Serial Communication on 1756-L6x Controllers Chapter 6
efficiency minimizes the number of times the radios must key-up to transmit,
which maximizes radio life and minimizes radio power consumption.
In contrast, DF1 half-duplex protocol requires five transmissions for the DF1
master to complete a read/write transaction with a DF1 slave—three by the
master and two by the slave.
The DF1 radio modem driver can be used in a pseudo master/slave mode with
any radio modems, as long as the designated master node is the only node that
initiates MSG instructions, and as long as only one MSG instruction is triggered
at a time.
For modern serial radio modems that support full-duplex data port buffering and
radio transmission collision avoidance, the DF1 radio modem driver can be used
to configure a masterless peer-to-peer radio network, where any node can initiate
communication to any other node at any time, as long as the nodes are within
radio range so that they receive transmissions from each other.
DF1 Radio Modem Limitations
These considerations must be made if you can implement the new DF1 radio
modem driver in your radio modem network:
• If the devices on the network are ControlLogix controllers, you must
configure them with the DF1 radio modem driver via
RSLogix 5000 software, version 17.01.02 or later or Logix Designer
application, version 21.00.00 or later. If not, then make sure that the nodes
can support the DF1 radio modem protocol.
• If each node receives the radio transmissions of each other node, being
within radio transmission/reception range and on a common receiving
frequency (via a Simplex radio mode or via one, common, full-duplex
repeater) the radio modems must handle full-duplex data port buffering
and radio transmission collision avoidance.
If so, you can take full advantage of the peer-to-peer message initiation
capability in each node (for example, the ladder logic in any node can
trigger a MSG instruction to any other node at any time).
If not all modems can handle full-duplex data port buffering and radio
transmission collision avoidance, you can use the DF1 radio modem driver.
Use the DF1 radio modem driver only if you limit MSG instruction
initiation to one master node who transmits to each other node.
• If not all nodes receive the radio transmission of each other node, you can
use the DF1 radio modem driver. Use the DF1 radio modem driver only if
you limit MSG instruction initiation to the node connected to the master
radio modem who transmits to each other radio modem in the network.