Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 216)

Publication AG-UM008C-EN-P - February 2005
6-12 Configuring MicroLogix 1000 Controllers
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 5 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 Poll Timeout The Poll Timeout is only used when the DF1 half-duplex slave is
initiating MSG instructions in ladder logic. This implies that the master
is most likely configured for Standard Polling Mode. The minimum
Poll Timeout value is dependent on the maximum master poll scan
rate. Since the master’s polling and the slave’s triggering of a MSG
instruction are asynchronous events, it is possible that in the instant
just after the slave was polled, the MSG instruction gets triggered. This
means the MSG instruction will remain queued-up for transmission
until the master has polled every other slave first. Therefore, the
minimum Slave Poll Timeout value is equal to the maximum master
poll scan rate rounded up to the next 20 ms increment.
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.
Minimum Poll Timeout = (maximum Master scan poll rate)