5902 Bell 202 Modem Hardware Manual
October 19, 2007
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If the CD LED flickers off during reception, you have a poor signal level or loose wiring.
You will lose data.
If the CD LED flickers on randomly, you have a noisy communication channel. You will
receive garbage data. Try adjusting the squelch level if using radios.
If the CD LED briefly flickers on at the end of a reception, increase the carrier loss delay by
adjusting the CL0 and CL1 switches.
If the CD LED flickers briefly on at the end of a transmission, increase the carrier detect
delay by adjusting the CD0 and CD1 switches.
For maximum performance, the carrier loss delays (CL switches) and carrier detect delays
(CD switches) should be adjusted to the shortest time period which provides reliable
communication. A flickering CD LED is a sure sign of problems and must be avoided.
Having said this, there is no point in increasing the carrier loss and carrier detect delays to
prevent a flickering CD LED if the cause of the flickering is low signal level or noise. If the
signal is too low or too noisy, data errors will occur even though the CD LED seems steady.
11.
Attempt to communicate. If there are errors further adjustments of the carrier detect and carrier
loss delays are likely necessary. If there are no communication errors, you can attempt to speed
up communication by reducing clear to send (CSH) hold, soft carrier turn-off (SCT) and
RTS/CTS delays as described below.
12.
You can attempt to speed up communication by reducing the clear to send (CSH) hold and soft
carrier turn-off (SCT) delays. Open the CSH switch. If the system still functions well, open the
SC0 switch. If it still functions well, close the SC0 switch and open the SC1 switch.
Most systems need only the SC0 switch closed. You can try opening both the SC0 and SC1
switches. If the system still works reliably, you do not need soft carrier turn-off. This is unlikely.
Most systems benefit from soft carrier turn-off. Use the shortest SCT time that provides reliable
operation.
13.
You can attempt to speed up communication by reducing the RTS/CTS delay. Open the CS0
switch. It the system still works, close the CS0 switch and open the CS1 switch. If is still works,
open both the CS0 and CS1 switches.
14.
Now that the modem delays are properly adjusted, you can add anti-streaming protection. If a
DTE fails to de-assert RTS for whatever reason, your communication system will be disabled
until the anti-streaming kicks in. You do not want anti-streaming to interfere with long messages
so use an anti-streaming time you are comfortable with.
Observe the maximum transmission time. Choose an anti-streaming time longer than the maximum
time. If the maximum message time is close to the anti-streaming time, use the next larger anti-
streaming time setting. This allows for variability in the message length. Set the AS0 and AS1
switches accordingly.
