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5.5.11
CD LED Always On in Radio System
The CD LED is always on or flickers – indicating carrier received – in a radio system.
An unsquelched radio receiver usually causes this problem. It prevents the modem from transmitting
due to the presence of carrier, and it causes a steady stream of garbage data to be received.
Adjust the radio's squelch setting if it has one. Use the radio frequency carrier detect (RCD) input
on the modem so that carrier is ignored unless RF carrier is detected.
5.5.12
CD LED Always On in 2 Wire System
The CD LED is always on or flickers – indicating carrier received – in a 2 wire system.
If garbage data is steadily received (RD LED on), the line is probably noisy. The source of the noise
must be removed. If this is a telephone line system, contact the telephone company. If this is a direct
wired system, look for noise sources near the cable run. Make sure the cable shield is grounded at
one end only.
If no garbage data is received (RD LED off) a modem on the network is continuously transmitting.
That modem is improperly configured for full duplex, or its DTE device is continuously asserting
RTS.
5.6
LED Indicators
The 5902 modem has seven status LEDs.
The LEDs are powered by the communication or SCADA controller module through the I/O bus.
The LEDs can be disabled to conserve power. Refer to the controller manual for more information.
LED
Color
TD
clear
RD
clear
CD
red
CS
red
RS
red
KEY
red
5902 Bell 202 Modem Hardware Manual
October 19, 2007
Function
The TD LED is on when the DTE is transmitting data to the
modem.
The RD LED is on when space is being received by the modem.
The CD LED is on when a received carrier is detected by the
modem. The CD LED status is affected by the carrier detection
and loss delays and by the soft carrier turn-off tone.
The CD LED status is the same as the DCD signal on the
RS-232 port.
The CS LED is on when the modem is ready to accept transmit
data from the DTE.
The CS LED status is the same as the CTS signal on the
RS-232 port.
The RS LED is on when the RTS signal on the RS-232 port is
asserted. It indicates the DTE wishes to transmit data.
The KEY LED is on when the KEY output is closed. It indicates
the modem is keying the radio to transmit data.
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