Rockwell Automation 1764-xxxx MICROLOGIX 1500 PROGRAMMABLE CONTROLLERS - Manual (Page 135)

Publication 1764-UM001B-EN-P - April 2002
Understanding Communication Protocols E-3
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.
Using Modems with
MicroLogix 1500
Programmable Controllers The types of modems that you can use with MicroLogix 1500
controllers include dial-up phone modems, leased-line modems, radio
modems and line drivers.
For point-to-point Full-Duplex modem connections that do not
require any modem handshaking signals to operate, use DF1
Full-Duplex protocol with no handshaking. For point-to-point
Full-Duplex modem connections that require RTS/CTS handshaking,
use DF1 Full-Duplex protocol with handshaking.
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.