Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 234)

Publication AG-UM008C-EN-P - February 2005
7-8 Configuring Logix Controllers
Configuration
Considerations for RTS
Send and Off Delays Through your programming software, the parameters RTS Send Delay
and RTS Off Delay give you the ability to set how long RTS is on prior
to transmission, as well as how long to keep it on after transmission is
complete. These parameters only apply when you select Half-Duplex
with or without continuous carrier. For maximum communication
throughput, leave these parameters at zero.
For use with half-duplex modems that require extra time to
turnaround or key-up their transmitter even after they have activated
CTS, the RTS Send Delay specifies (in 20 millisecond increments) the
amount of delay time after activating RTS to wait before checking to
see if CTS has been activated by the modem. If CTS is not yet active,
RTS remains active, and as long as CTS is activated within one second,
the transmission occurs. After one second, if CTS is still not activated,
then RTS is set inactive and the transmission is aborted.
For modems that do not supply a CTS signal but still require RTS to be
raised prior to transmission, jumper RTS to CTS and use the shortest
delay possible without losing reliable operation.
If an RTS Send Delay of 0 is selected, then transmission starts as soon
as CTS is activated. If CTS does not go active within one second after
RTS is raised, RTS is set inactive and the transmission is aborted.
Certain modems will drop their carrier link when RTS is set inactive
even though the transmission has not quite been finished. The RTS
Off Delay parameter specifies, in 20 millisecond increments, the delay
between when the last serial character is sent to the modem and when
RTS is deactivated. This gives the modem extra time to transmit the
last character of a packet.
Configuring a
Standard-Mode DF1
Half-Duplex Master Station Choose standard-communication mode if you want to query slave
stations for information based upon user-configured polling lists. This
mode is used most often in point-to-multipoint configurations because
it allows polled report-by-exception (page 1-4), slave station-to-station
messaging (page 1-5) and slave programming over the telemetry
network (Chapter 11) to be implemented. In addition, in this mode
the master station maintains an active node table which allows an
MMI or programming terminal to immediately identify which slave
nodes can currently communicate and which nodes cannot.
ATTENTION
For almost all modem applications, the RTS Off
Delay should be left at 0. Never Select an RTS Off
Delay that is greater than the RTS Send Delay in the
other devices on the network, or you may incur two
devices trying to transmit simultaneously.