Rockwell Automation Publication 5069-UM003B-EN-P - January 2020
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Compact 5000 I/O Serial Module Features
Chapter 3
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 before transmission and
how long to keep it on after transmission is complete. These parameters only
apply when you select half-duplex modem 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
before 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 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.
IMPORTANT
• 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 can incur two devices that try
to transmit simultaneously