Publication 1747-RM001G-EN-P - November 2008
SLC Communication Channels 13-89
Full Duplex Modem - DTR and RTS are always active except at the
following times. If DSR goes inactive, modem lost bit (S:5/14) is turned on
immediately. While DSR is inactive, neither reception nor transmission is
performed. The processor does not monitor DCD. Transmission requires
CTS & DSR inputs to be active. .
Half Duplex without Continuous Carrier - DTR is always active and RTS is
only active during transmissions (and any programmed delays before and after
transmissions). The processor does not monitor DCD.
If DSR goes inactive, RTS is dropped. The modem lost bit (S:5/14) is turned
on immediately. While DSR is inactive, neither receptions nor transmissions
are performed. Transmission requires two inputs, CTS and DSR, to be active.
Whenever DSR is active, the modem lost bit is reset.
RTS Send Delay and RTS Off Delay Parameters
Through your programming software, the parameters RTS Send Delay and
RTS Off Delay give you the flexibility of selecting modem control during
transmissions. These parameters only apply when you select half-duplex
modem with or without continuous carrier.
For use with half-duplex modems that require extra time to “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 at all, tie RTS to CTS and use the
shortest delay possible without losing reliable operation.
TIP
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 1 second after RTS is raised, RTS is set inactive and
the transmission is aborted.
Certain modems will drop their carrier link when RTS is lost
even though the transmission has not been finished yet. 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.
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