CTI Products EXB-232 Asynchronous Serial System Extender - Manual (Page 20)

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4. EXB Module Usage
Once properly connected and configured for use, the EXB module is simple to operate. Run-
time operation of the EXB module is completely automatic.
4.1 EXB-TELCO Usage
After power up or reset, an EXB module set to Leased-Line Originate mode will immediately go
off hook and emit a cyclic calling tone to the telephone circuit. An EXB module set to Leased-
Line Answer mode will go off hook and wait for detection of the calling tone from the distant
end. When this calling tone is detected, the modem training sequence begins. This training
sequence determines telephone circuit characteristics, sets appropriately equalization parameters
and other housekeeping items, and concludes with the "CD" (carrier detect) LED illuminating.
Within 2 seconds after this LED lights, data packets can flow across the modem connection and
the simultaneous voice/data facility is enabled to the AUDIO port.
The elapsed time between training sequence start and end (carrier detect) is tracked by a timer
inside each EXB unit. If the time reaches 20 seconds and training has not concluded, the EXB
units will automatically restart the calling tone sequence. Once a connection is established
between the two EXB modems, any loss of carrier will be detected by both EXB modules and
cause them to automatically restart the calling tone sequence. Data entering the EXB module
while the modem is in the calling tone or training sequence is not buffered.
4.2 EXB-Serial Usage
After power up or reset, the EXB-Serial module is ready to begin transferring data over the
asynchronous RS-232 port(s). Data received on the Network port is immediately transmitted on
the RS-232 ports. Data received on the RS-232-ports is transmitted on the Network port. If both
RS-232 ports are enabled, any data received on one port is transmitted on the other RS-232 port,
as well as the Network port.