Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 233)

Publication AG-UM008C-EN-P - February 2005
Configuring Logix Controllers 7-7
Modem Control Line
Operation The following sections explain the operation of the Logix controller
serial port control line selections.
No Handshake Selected
DTR is always active (high) and RTS is always inactive (low).
Receptions and transmissions take place regardless of the states of
DSR, CTS, or DCD inputs. Only make this selection when the Logix
controller is directly connected to another device that does not require
handshaking signals.
Full-Duplex Selected
DTR and RTS are always active except:
•
If DSR goes inactive, both DTR and RTS are dropped for 1 to 2
seconds, then reactivated. The modem lost minor fault comes on
immediately. While DSR is inactive, the state of DCD is ignored.
Neither receptions nor transmissions are performed.
•
If DCD goes inactive while DSR is active, then receptions are not
allowed. If DCD remains inactive for 9 to 10 seconds, DTR is set
inactive. At this point, the modem lost minor fault also comes
on. If DSR remains active, DTR is raised again in 5 to 6 seconds.
Reception requires DSR and DCD to be active. Transmission requires
all three inputs (CTS, DCD, and DSR) to be active. Whenever DSR and
DCD are both active, the modem lost minor fault goes off.
Half-Duplex Selected with Continuous Checked
DTR is always active and RTS is only activated during transmissions
(and any programmed delays before or after transmissions). The
handling of DCD and DSR are exactly the same as with Full-Duplex
Modem. Reception requires DSR and DCD to be active. Transmissions
require CTS, DCD and DSR to be active. Whenever DSR and DCD are
both active, the modem minor fault goes off.
Half-Duplex Selected with Continuous Carrier Unchecked
This is exactly the same as Half-Duplex Modem with Continuous
Carrier checked, except monitoring of DCD is not performed. DCD is
still required for receptions, but is not required for transmissions.
Transmissions still require CTS and DSR. Whenever DSR is active, the
modem lost minor fault goes off.