data terminal ready (dtr)
the terminal sets the dtr line on (active) to gain control over the fcd-2 and start a configuration/monitoring session.
when the dtr is on, the front panel controls are disabled, and the lcd displays a message that notifies the operator that fcd-2 is under remote management:
terminal on line.
the dtr line is off (inactive) when terminal control is not required. this ends the terminal control connection, and returns the control to the fcd-2 front panel. if password protection is used, the password must be entered again the next time the dtr line is set on to start a new session.
request to send (rts)
the rts is normally on (active) when the supervision terminal is in session.
when the rts line is off (inactive), fcd-2 interprets any data received from the terminal on the td line as mark.
clear to send (cts)
the state of the cts line is determined by the cts parameter:
1 on - the cts line is always on (active).
2 =rts - the cts line follows the rts line.
data carrier detect (dcd)
the state of the dcd line depends on the communication address (node number):
1 when the node address is 0, the dcd line is always on (active).
2 when a non-zero node address is used, the dcd line becomes on (active) when data is detected on the rd line, provided fcd-2 recognizes its own address in the data stream.
to simulate dte operation, the delay between these events can be set by the user (by means of dcd-delay parameter).
ring indicator (ri)
the ri is used only with dial-up modems (when the hayes mode is enabled).
the ri line is normally off (inactive) and switches to the on (active) state when the modem attached to the fcd-2 sp connector detects an incoming call see also the dsr line.
data set ready (dsr)
usually, the dsr line is configured to track the dtr line. in this case, if the supervisory port interface is dte, the dsr line will be set to on for 5 seconds when the ri line is on while the dtr line is off.
if the supervisory port interface is dce, the dsr line can also be configured to be continuously on. however, if the dtr line switches to off, the dsr line will also switch to off for 5 seconds.
in addition, fcd-2 always sets dsr off (inactive) for 5 seconds when the exit command is executed, or the disconnect time-out expires.