Allen-Bradley micrologix 1500, User Manual, Page: 110 / 149

Publication 1764-UM001A-US-P
E-6 Understanding Communication Protocols
DF1 Half-Duplex Example Network
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 1500
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
Rockwell Software RSLinx 2.0 (or
higher), SLC 5/03, SLC 5/04, and
SLC 5/05, or PLC-5 processors
configured for DF1 Half-Duplex
Master.
DF1 Half-Duplex Protocol
MicroLogix 1500 with
1764-LSP or 1764-LRP
Processor (Slave)
SLC 5/03 (Slave)
MicroLogix
1000 (Slave)
MicroLogix 1500 with
1764-LRP Processor (Slave)
MicroLogix
1200 (Slave)
Modem
NOTE
It is recommended that isolation (1761-NET-AIC) be used
between channel 0 of the MicroLogix controller and the modem.
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 seconds. 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.