176 Rockwell Automation Publication 1766-UM001O-EN-P - September 2021
Appendix E Connect to Networks via RS-232/RS-485 Interface
DF1 Full-Duplex Protocol DF1 Full-Duplex protocol provides a point-to-point connection between two
devices. DF1 Full-Duplex protocol combines data transparency (American
National Standards Institute ANSI – X3.28-1976 specification subcategory D1)
and 2-way simultaneous transmission with embedded responses
(subcategory F1).
The MicroLogix controller supports the DF1 Full-Duplex protocol via RS-232
connection to external devices, such as computers, or other controllers that
support DF1 Full-Duplex.
DF1 is an open protocol. See DF1 Protocol and Command Set Reference
Manual, publication 1770-RM516
, for more information.
DF1 Full-Duplex protocol (also referred to as DF1 point-to-point protocol) is
useful where RS-232 point-to-point communication is required. DF1 protocol
controls message flow, detects and signals errors, and retries if errors are
detected.
Example DF1 Full-Duplex Connections
For information about required network connecting equipment, see
Chapter 4
.
DF1 Half-Duplex Protocol DF1 Half-Duplex protocol is a multi-drop single master/multiple slave
network. DF1 Half-Duplex protocol supports data transparency (American
National Standards Institute ANSI – X3.28-1976 specification subcategory D1).
In contrast to DF1 Full-Duplex, communication takes place in one direction at
a time. You can use the RS-232/RS-485 port on the MicroLogix as both a Half-
Duplex programming port and a Half-Duplex peer-to-peer messaging port.
DF1 Half-Duplex Operation
A DF1 Half-Duplex master device initiates all communication by “polling” each
slave device. The slave device may only transmit when it is polled by the
master. It is the master’s responsibility to poll each slave on a regular and
sequential basis to allow slave devices an opportunity to communicate.
An additional feature of the DF1 Half-Duplex protocol is that it is possible for a
slave device to enable a MSG write or read to/from another slave. When the
initiating slave is polled, the MSG is sent to the master. The master recognizes
that the message is not intended for it, but for another slave, so the master
immediately forwards the message to the intended slave. The master does this
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