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Advanced Modem Concepts
Changing Modem-to-Modem
Connection Data Rates
Your modem is capable of communicating with other modems at
data rates of 300, 1200, 2400, 4800. 7200. 9600. 12000, or
14400 bits per second (bps). When you place a call to another
modem, the settings of two AT commands (B and N) and two
S-Registers (S37 and S109) are used to determine the data rate
of that connection.
S-Register S37 is used to set the maximum allowable data rate.
S-Register S109 is used to select all the permitted data rates.
The B command is used to select whether the modem is
configured as a CCITT or BELL modem. The N command is
used to select whether the modems may connect only at a
single data rate (N0), or whether the modems may connect at a
lower data rate (N1).
When the N0 command is used, the modems can only connect
if the answering modem supports the data rate specified in
S-Register S37 of the originating modem (the one which places
the call). If the answering modem cannot support the data rate
specified by the originating modem, no connection will be made.
When the N1 command is used (the default setting from the
factory), the modems will first attempt to connect at the data
rate specified by S37. but will fall back to a lower data rate if
required by the receiving modem.
If you would like to know more about how the modem uses
modulations and data rates, refer to the information on the B
and N commands and S-Registers S37 and S109 in Chapter 4.
Issue 1 November 1994
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D-1
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