68 Rockwell Automation Publication 1766-UM001I-EN-P - June 2015
Chapter 4 Communication Connections
Connecting to a DF1 Half-Duplex Network
When a communication port is configured for DF1 Half-Duplex Slave, available
parameters include the following:
DF1 Half-Duplex Configuration Parameters
Parameter Options
Baud Rate 300, 600, 1200, 2400, 4800, 9600, 19.2 KBps, 38.4 KBps
Parity none, even
Node Address 0...254 decimal
Control Line no handshaking, half duplex modem (RTS/CTS handshaking, no handshaking (485 network)
Error Detection CRC, BCC
EOT Suppression enabled, disabled
When EOT Suppression is enabled, the slave does not respond when polled if no message is queued. This saves
modem transmission power and time when there is no message to transmit.
Duplicate Packet (Message)
Detect
enabled, disabled
Detects and eliminates duplicate responses to a message. Duplicate packets may be sent under noisy communication
conditions if the sender’s Message Retries are not set to 0.
Poll Timeout (x20 ms) 0...65,535 (can be set in 20 ms increments)
Poll Timeout only applies when a slave device initiates a MSG instruction. It is the amount of time that the slave
device waits for a poll from the master device. If the slave device does not receive a poll within the Poll Timeout, a
MSG instruction error is generated, and the ladder program needs to requeue the MSG instruction. If you are using a
MSG instruction, it is recommended that a Poll Timeout value of zero not be used. Poll Timeout is disabled when set to
zero.
RTS Off Delay (x20 ms) 0...65,535 (can be set in 20 ms increments)
Specifies the delay time between when the last serial character is sent to the modem and when RTS is deactivated.
Gives the modem extra time to transmit the last character of a packet.
RTS Send Delay (x20 ms) 0...65,535 (can be set in 20 ms increments)
Specifies the time delay between setting RTS until checking for the CTS response. For use with modems that are not
ready to respond with CTS immediately upon receipt of RTS.
Message Retries 0...255
Specifies the number of times a slave device attempts to resend a message packet when it does not receive an ACK
from the master device. For use in noisy environments where message packets may become corrupted in
transmission.
Pre Transmit Delay
(x1 ms)
0...65,535 (can be set in 1 ms increments)
•When the Control Line is set to no handshaking, this is the delay time before transmission. Required
for 1761-NET-AIC physical Half-Duplex networks. The 1761-NET-AIC needs delay time to change from
transmit to receive mode.
•When the Control Line is set to DF1 Half-Duplex Modem, this is the minimum time delay between
receiving the last character of a packet and the RTS assertion.
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