COURIER HIGH SPEED MODEMS
Data Mode Operations 4-21
Data Rates
The modem can be set to a fixed or variable serial port rate. A
fixed rate sets the modem for the highest possible throughput
and provides the best performance. A variable rate allows the
modem to switch to match the more limited rate on the phone
connection.
Your software must support fixed or variable serial port rates,
and must be set to either of the two settings. NOTE: Your
software may refer to these options with terms like locked serial
port (fixed rate) or autobaud (variable rate).
Most communications programs support variable rates, but not
all software supports fixed rates.
WARNING: To connect above 9600 bps, the serial port rate
must be 19.2K, 38.4K, 57.6K, or 115.2K bps. If the local
computer is limited to 9600 bps, V.32 terbo modems are limited
to 9600 bps maximum, that is, V.32. Disable V.32 terbo
modulation so that the modem does not switch its serial port
rate up higher than 9600 bps. Do this by setting Register S34 to
3 (S34=3) and including that setting in the defaults you write to
nonvolatile memory, as shown in Setting/Using Defaults earlier
in this chapter.
&Bn Serial port rate variable or fixed.
&B0 Variable rates. When the modem switches its connection
rate to connect with a modem operating at a different
rate, it also switches its serial port rate. The software or
terminal also switches serial port rates to match the
connection rate.
&B1 Fixed rate. Default. The modem always communicates
with the terminal or computer at the rate at which you
have set the terminal or software, regardless of the
connection rate. For the greatest throughput, set the
serial port to 115.2K, 57.6K, 38.4K bps for high speed
calls and to at least 9600 bps for 2400-bps calls.
This setting is not affected by the &N setting. However,
the serial port rate must be equal to or higher than the &Nn
rate.
