Chapter 3
LEDs and Controls
T
his chapter describes the LEDs and controls on the modem.
Front Panel LEDs
Table 3-1 describes the LEDs on the modem front panel.
Table 3-1. Front Panel LEDs
LED
Status
PWR
ON = power is being supplied to the modem.
TM
ON = the rotary switch is turned to Analog or Digital Loopback, or the switch is in the Test
Pattern transmit mode or Self Test mode and no error is detected.
CD
ON = the modem is detecting a valid carrier.
RD
ON = data is being received or receive data line is in a space condition.
RS
ON = the Request-to-Send line from the DTE is ON.
CS
ON = the Clear-to-Send line from the modem is ON.
TD
ON = data to be transmitted is being furnished to the modem.
Front Panel Test Switch
The modem front panel has a five-position rotary switch that lets you select the modem’s operating mode. The five
switch positions are:
DATA
use this position for normal data transmissions.
AL
(Analog Loopback)
this position prepares the modem for testing by the local terminal device. The
transmitter output of the modem is disconnected from the output coupling transformer and connected to the
modem receiver input. See Figure 3-1.
DL
(Digital Loopback)
this position configures the modem to loop back received data to the transmitter and
transmit the data to the remote end. The RS-232-C interface to the terminal is not active during this test. See
Figure 3-2.
ST
(Self Test)
this position inhibits the modem from transmitting and receiving data on the COMM LINE.
The RS-232-C interface to the terminal is not active during this test. See Figure 3-3.
The test pattern (dot pattern) passes through the transmitter, loops back into the receiver, is demodulated, and is
checked for errors. If errors occur, the
TM
LED turns OFF and remains OFF for a period of time that depends
on the pattern generator baud rate.
In Analog Loopback and Self Test modes, the received analog data is buffered, amplified by 16 dB (if output
level is set to 0 dB), and routed out on the transmit analog pair.
TTP
(Transmit Test Pattern)
this setting forces the transmitter on and transmits data from the test generator
to the COMM LINE. The RS-232-C interface lines (RTS, CTS, and Transmit Data) to the transmitter are not
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