Rockwell Automation Publication 1766-UM001O-EN-P - September 2021 177
Appendix E Connect to Networks via RS-232/RS-485 Interface
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 or MicroLogix 1500 controller, and RSLinx
software (version 2.x and higher).
DF1 Half-Duplex supports up to 255 devices (address 0…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.
Figure 71 - Example DF1 Half-Duplex Connections
Considerations When Communicating as a DF1 Slave on a Multi-drop Link
When communication is between either your programming software and a
MicroLogix Programmable Controller or between two MicroLogix 1400
Programmable Controllers via slave-to-slave communication on a larger multi-
drop link, the devices depend on a DF1 Half-Duplex Master to give each of
them access in a timely manner. As the number of slave devices increase, the
time between when slave devices are polled also increases. This increase in
time may also be large if you are using low baud rates. As these time periods
grow, you may need to increase the poll timeout and reply timeout values for
slave devices.
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
RSLinx software 2.0 (or later), SLC 5/03,
SLC 5/04, and SLC 5/05, PLC-5, MicroLogix 1400,
or MicroLogix 1200 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)
IMPORTANT If a program download is started when using DF1 Half-Duplex, but then is
interrupted due to electromagnetic interference or other events,
discontinue communications to the controller for the ownership timeout
period and then restart the program download. The ownership timeout
period is 60 s. After the timeout, you can re-establish communications with
the processor and try the program download again. The only other way to
remove program ownership is to cycle power on the processor.
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