Rockwell Automation 1766-Lxxxx MicroLogix 1400 Programmable Controllers User Manual - Manual (Page 226)

186 Rockwell Automation Publication 1766-UM001H-EN-P - May 2014
Appendix E Connecting to Networks via RS-232/RS-485 Interface
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.
Using Modems with MicroLogix Programmable Controllers
The types of modems you can use with MicroLogix controllers include the
following:
• dial-up phone modems.
A MicroLogix controller, on the receiving end of the dial-up connection,
can be configured for DF1 Full-Duplex protocol with or without
handshaking. The modem connected to the MicroLogix controller should
support auto-answer. The MicroLogix 1400 supports ASCII out
communications. Therefore, it can cause a modem to initiate or disconnect
a phone call.
• leased-line modems.
Leased-line modems are used with dedicated phone lines that are typically
leased from the local phone company. The dedicated lines may be in a
point-to-point topology supporting Full-Duplex communications
between two modems or in a multi-drop topology supporting
Half-Duplex communications between three or more modems.
• radio modems.
Radio modems may be implemented in a point-to-point topology
supporting either Half-Duplex or Full-Duplex communications, or in a
multi-drop topology supporting Half-Duplex communications between
three or more modems. MicroLogix 1400 also supports DF1 Radio
Modem protocol.
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.