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Rockwell Automation Publication 2080-UM002N-EN-E - November 2022 337
Appendix G Connect to Networks using DF1
Considerations When Communicating as a DF1 Slave on a Multi-drop
Link
When communication is between either your programming software and a Micro800 controller
or between two Micro800 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 increases, 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 Micro800 Programmable Controllers
The types of modems you can use with Micro800 controllers include the following:
• Dial-up phone modems.
A Micro800 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
Micro800 controller should support auto-answer.
• 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. Micro800 controllers also
support DF1 Radio Modem protocol.
• Line drivers.
Line drivers, also called short-haul modems, do not actually modulate the serial data,
but rather condition the electrical signals to operate reliably over long transmission
distances (up to several miles). Line drivers are available in Full-Duplex and Half-Duplex
models.
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.
For radio modem connections, use DF1 Radio Modem protocol, especially if store and forward
capability is required.
For general multi-drop modem connections, or for point-to-point modem connections that
require RTS/CTS handshaking, use DF1 Half-Duplex slave protocol. In this case, one (and only
one) of the other devices must be configured for DF1 Half-Duplex master protocol.
IMPORTANT Program download is not supported in DF1 Half-Duplex and Radio
Modem for Micro850 (2080-L50E) and Micro870 (2080-L70E) controllers
firmware revision 20 or later.
Micro850 (2080-L50E) and Micro870 (2080-L70E) controllers support RTS/CTS
modem handshaking when configured for DF1 Full-Duplex protocol with the control
line parameter set to Full-Duplex Modem Handshaking or DF1 Half-Duplex slave
protocol with the control line parameter set to Half-Duplex Modem.
These controllers also support DCD (Data Carrier Detect) line for DF1 Radio Modem
protocol. No other modem handshaking lines (such as Data-Set™ Ready and Data
Terminal Ready) are supported by Micro800 controllers.