Full-Duplex (Point-To-Point; Df1 Half-Duplex Protocol - Allen-Bradley SLC 500 User Manual

Allen-Bradley PLCs

Full-Duplex (Point-to-Point)

DF1 Half-Duplex Protocol

DF1 half-duplex protocol provides a multi-drop single master/multiple
slave network. In contrast to the DF1 full-duplex protocol,
communication takes place in one direction at a time. You can use
channel 0 as a programming port, or as a peer-to-peer port using the
MSG instruction.
In half-duplex mode, the SLC 5/03, SLC 5/04, and SLC 5/05 processors
can be either master or slave devices. As a master device, the
processor polls each slave on the network on a regular and sequential
basis. The master also supports routing of data packets from one
slave to another, or slave-to-slave communication. As a slave device,
the processor can send data packets when polled by the master
device, which initiates all communication with slave devices.
If the master device has no data to send, it can still receive data from
the slave device. To do this, the master sends out a poll packet
addressed to the slave. If the slave has data to send, it does so in
response to the poll packet. Otherwise, the slave sends a simple
two-byte response, so that the master knows that it is active.
Several Allen-Bradley products support half-duplex master protocol.
They include the Enhanced PLC-5 processors, and SLC 5/03, SLC 5/04,
and SLC 5/05 processors. WINtelligent Linx and RSLinx (2.0 or
higher) from Rockwell Software, Inc. also support half-duplex master
protocol.
DF1 Half-duplex supports up to 255 slave devices (addresses 0 to 254)
with address 255 reserved for master broadcasts. The SLC 5/03, SLC
5/04, and SLC 5/05 support broadcast reception, but cannot initiate a
broadcast command.
RS-232 Communication Interface
Modem
Modem
SLC 5/03
(1747-L532)
1747-CP3
Publication 1747-UM011C-EN-P - December 2001
B-5
SLC 5/03
(1747-L532)