Table of Contents
Advertisement
5.5.7
Missing End of Long Message
The end of a long message is always missing. Short messages are received correctly.
This problem occurs when the transmitting modem's anti-streaming time is too short. Confirm this
by observing the transmitting modem turn off the CD and KEY LEDs while the RS LED is still on.
Increase the anti-streaming time, or disable it if necessary, to correct this problem.
5.5.8
RS LED Always On; All Other LEDs Off.
The modem seems to be dead. The RS LED is on but the CS and KEY LEDs are off.
This situation indicates the modem has shut off due to anti-streaming. Either the anti-streaming time
period is too short for the message length, or the DTE is not de-asserting RTS at the end of each
transmission.
Try increasing the anti-streaming time or disabling it if necessary, to correct this problem. If this
does not correct the problem, the DTE device configuration must be modified. If the DTE does not
provide RTS/CTS control, the F Option may be added to compensate for this problem.
5.5.9
DTE Transmits Too Soon after Receive
The DTE device transmits a new message too soon after data is received. The start of the
message is lost, because the receiving modem is not ready to receive.
Increase the carrier loss delay if soft carrier turn-off is not used (adjust CL0 and CL1). The modem
will not allow transmission until carrier is absent (unless configured for constant carrier operation).
If soft carrier turn-off is used, increase the RTS/CTS delay to transmit a pause between carrier start
and data transmission.
5.5.10
CD LED Always On in Master Modem
The carrier detect (CD) output of a constant carrier modem is always on, even though slave
modems are not transmitting.
This problem is usually caused by crosstalk from the transmit pair to the receive pair. The
transmitted carrier is coupled into the receive wiring and is detected. Although the constantly
received carrier will not interfere with transmission, it may interfere with reception from the slaves.
It also make it difficult to judge how effectively carrier is being received from the slave modems.
Reduce the modem receive sensitivity by adjusting the RX GAIN potentiometer. Reducing the
transmit level – by adjusting the TX GAIN potentiometer – may also work, although this will reduce
the signal being transmitted to the slave modems.
A very noisy line can cause this problem. To determine if this is the case, disconnect the transmit
wire pair from the modem. Ensure that none of the slave modems are continuously transmitting. If
the carrier persists, the line is too noisy.
This problem can also be caused by trying to operate a full duplex, constant carrier modem on a two
wire network. Full duplex constant carrier always requires four wires. Check that the 2 WIRE switch
is open, and the 4 WIRE switch is closed.
5902 Bell 202 Modem Hardware Manual
October 19, 2007
35
Advertisement
Table of Contents
