Black Box 32144 Manual page 154

MODEM 32144
Where line conditions are
atypical, it may be necessary to
adjust the equalizers to optimize
the signal quality. If adjustment is
necessary, refer to the quality
screen for guidance; this screen
shows a relative indication of the
signal quality, in both numeric
and graphic form.
Trellis Code
Hayes, V.25 bis, Dumb, Leased line
modes (except V.33)
Trellis coding provides
performance advantages for all
modulation patterns. The modem's
CCITT compliant trellis coder is
normally enabled at speeds of
7200 bps and above, but may be
negotiated off by a modem that is
not equipped with a trellis coder at
9600 bps. The trellis code option
allows the user to enable or disable
the trellis coder.
Transmitter Clocking
All modes
This option selects one of three
possible sources for the transmitter
timing signal:
INTERNAL. The timing of the
modem and data terminal
transmitting circuits is provided
by an internal clock within the
modem.
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RECEIVED (RX-CLK). The
timing of the data received from
the remote modem is used to
control the timing of the trans-
mitted data. This timing mode is
used if the modem's transmit
timing must be controlled by a
remote source.
EXTERNAL. The timing of
the modem and data-terminal
transmitting circuits is synchro-
nized to an external clock from
within the data terminal and is
provided to the modem via the
DTE connector pin 24. This
mode of clocking is used if the
DTE must be in control of the
modem's transmit timing. The
modem's minimum and maximum
speed must be set to approximately
the same speed as the DTE clock.
(To set the maximum speed, use
the Speed Limit option.)
T1 Timer
Hayes, V.25 bis, Dumb modes
The T1 Timer option is only
effective if the Summary Setup
Multimode Handshake option
is set to 0 (T1 timer).
The T1 Timer option determines
how long the ALX modem will
attempt to handshake with a calling
V.32 modem before falling back to
a lower speed. The available T1
Timer settings are 0, 0.3, 0.8, 1.6
and 3.0 seconds.