Specifications

Rockwell Automation Publication AG-SG001G-EN-P - April 2015 33
Choosing a Telemetry Network Chapter 2
Choosing a Protocol
A protocol governs the format of data transmission between two or more
stations, including handshaking, error detection, and error recovery. When
choosing a protocol, select one that best fits your application's:
• Connection topology
• Transmission mode
• Other application requirements, such as connections to existing
equipment
If all the control products used in your application are Allen-Bradley products,
use the DF1 serial protocol or an EtherNet/IP network because they provide
benefits, such as the following:
• Remote data table monitoring and online programming using standard
Rockwell Software programming software
• Remote station-to-remote station messaging
• A more cost-effective solution since the protocol is built into
Allen-Bradley products
DF1 protocol is an asynchronous, byte-based protocol. DF1 protocol options are
described below.
DF1 Half-duplex Protocol
Using DF1 half-duplex protocol provides these advantages:
• You do not have to program the master station to read blocks of data from
each remote station to determine if the remote station has new data. Get
data from remote stations just by polling them. Remote stations can collect
data on their own and have the message blocks waiting to send when the
master station polls them.
• You can perform remote station-to-remote station messaging through the
master station without any special ladder logic in the master and without
increased processing time.
• You can program remote stations over the telemetry network without
interrupting the master station's normal control and data acquisition
functions.
• You can program the master to broadcast write a block of data to all remote
stations simultaneously for synchronization purposes.
If your transmission mode is Then choose this type of protocol
Bidirectional but one direction at a time DF1 half-duplex or DNP3
Simultaneously bidirectional DF1 full-duplex or DNP3
Peer-to-peer DF1 radio modem or EtherNet/IP