Modem led indicators, Carrier detect (cd), Clear to send (cts) – Multi-Tech Systems MT202TD 1200 User Manual
Page 10: Data set ready (dsr), Led indicators, Request to send (rts)

MT202TD User Guide
10
Modem LED Indicators
Figure 2-2. LED Display
The MT202TD has seven diagnostic LED indicators. They are:
TD
Transmit Data - This LED blinks when data is being
transmitted: on for a space; off for a mark. The state of
this LED matches the TD circuit on Pin 2 of the RS-
232C/V.24 interface.
RD
Receive Data - This LED blinks when data is being
received: on for a space; off for a mark. The state of this
LED matches that of the RD circuit on Pin 3 of the RS-
232C/V.24 interface.
CD
Carrier Detect - This LED lights when a valid carrier
tone has been detected.
CTS
Clear to Send - This LED lights when the modem
responds to a Request to Send signal after a fixed
delay. The terminal equipment may start transmitting
data after this signal is on (high).
RTS
Request to Send - This LED lights when the Request
to Send signal from the DTE is on.
DSR
Data Set Ready - This LED lights when the modem is
powered on.
TM
Test Mode - This LED lights when the modem is in Test
Mode.