Introduction / Modem Operation - Polycom Vortex EF2241 Application Note

I
NTRODUCTION
You may connect an external modem to a Vortex device (EF2280, EF2241,
EF2201, EF2210, EF2211) to perform remote diagnostics. The basic requirement
for the modem is that is should be capable of connecting at 9600 bps.
The key to making a reliable modem connection is that you have to force the
modem's to handshake at 9600 bps. If you do not, the Autoscanning process
will hang as buffers in the modems are not filled with data fast enough. If your
modem has a loudspeaker, you should be able to listen to the handshaking
signals. If the signals sound like you are trying to connect at 33600 bps or
higher, chances are the Autoscanning process will hang as the modems think
that they can send data back and forth at that rate. The EF2280's and EF2241's
will only be able to send data at 9600 bps to the modem. Even with RTS
enabled between the modem and the EF2280/EF2241, the RS-232 buffer of the
modem will still underflow which will normally cause the modem to disconnect
the call.
You may leave all devices connected to the RS-232 ports of the EF
Devices (control system, IR-10, PC, etc.) while using the modem.
However, if that device does not parse the incoming data and clear
its buffers, the EF Devices will not be able to successfully send
data to the modem. This would normally happen if a PC was
connected to an EF Device, but software to interface with the
Comm port (Conference Composer. Hyperterminal, etc.) was not
open during a remote autoscan of the system via the modem. If
Conference Composer, Hyperterminal, etc. are open during the
remote autoscan via the modem, you will not experience any
problems.
The above comments do not apply is you are going to use a 3Com
(U.S. Robotics) modem. Please see the 3Com (U.S. Robotics)
Modem Bug page for more information.
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