Rockwell Automation 1766-Lxxxx MicroLogix 1400 Programmable Controllers User Manual - Manual (Page 225)

Rockwell Automation Publication 1766-UM001H-EN-P - May 2014 185
Connecting to Networks via RS-232/RS-485 Interface Appendix E
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
automatically; you do not need to program the master to move data between slave
nodes. This slave-to-slave transfer can also be used by programming software to
allow slave-to-slave upload and download of programs to processors (including
the master) on the DF1 Half-Duplex link.
MicroLogix 1400 can act as the master or as a slave on a Half-Duplex network.
When the MicroLogix 1400 is a slave device, a master device is required to “run”
the network. Several other Allen-Bradley products support DF1 Half-Duplex
master protocol. They include the SLC 5/03™ and higher processors, enhanced
PLC-5 processors, MicroLogix 1200/1500 and Rockwell Software RSLinx
(version 2.x and higher).
DF1 Half-Duplex supports up to 255 devices (address 0 to 254) with address 255
reserved for master broadcasts. As a DF1 Half-Duplex slave device, the
MicroLogix supports broadcast reception. As a DF1 Half-Duplex master, the
MicroLogix 1400 supports both the reception and initiation of broadcast write
commands (via the MSG instruction). The MicroLogix also supports
Half-Duplex modems using RTS/CTS hardware handshaking.
Example DF1 Half-Duplex Connections
TERM A B COM SHLD CHS GND TX
TX PWR
TX
DC SOURCE
CABLE
EXTERNAL
TERM A B COM SHLD CHS GND TX
TX PWR
TX
DC SOURCE
CABLE
EXTERNAL
TERM A B COM SHLD CHS GND TX
TX PWR
TX
DC SOURCE
CABLE
EXTERNAL
Rockwell Software RSLinx 2.0 (or
later), SLC 5/03, SLC 5/04, and SLC
5/05, PLC-5, MicroLogix 1400, or
MicroLogix 1000/1200/1500
processors configured for DF1
Half-Duplex Master. RS-232
(DF1 Half-Duplex Protocol)
MicroLogix
1500 (Slave) SLC 5/04
(Slave) MicroLogix
1000 (Slave) SLC 5/03 with
1747-KE Interface
Module (Slave) MicroLogix
1200 (Slave)
Modem
MicroLogix
1400 (Slave)
44596