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536EX Chipset Developer’s Manual 11
Intel Confidential
Introduction
The modem recognizes AT commands from the DTE at any valid data rate from 300 bps to 115,200
bps (that is, the modem autobauds up to 115,200 bps); however, the DTE should use the data rate
specified for each mode according to the transmitting direction—DTE-to-modem (Table 1) or
modem-to-modem (Table 2). The V.90 and V.92 data rates are effective only in DCE-to-ISP
connections.
Each command may have one or more parameters associated with it. If a parameter is not sent for a
command requiring a numeric parameter, then the modem assumes a zero (‘0’) parameter (only if
zero is a valid parameter for the command). For example, ATZ and ATZ0 commands perform
identical functions (that is, the modem sees ‘ATZ ’ and automatically uses the ‘0’ parameter during
processing the command). Other commands do not use parameters.
1.4 AT Commands Overview
The AT command set and S-registers are divided into four categories: data, Group 3 fax, voice, and
V.42/MNP. Summaries of all commands are provided later on in this chapter.
Table 1. DTE-to-DCE Data Rates for Each Mode
Mode Data Rate (bps) Affected Data
Data (V.34) 2400–115,200
DTE-to-modem data rate Data (V.90) 28,800–115,200
Data (V.92) 28,800–115,200
Fax 19,200
Voice 19,200–115,200
AT commands, playback and record modes
(varies according to compression type)
Table 2. DCE-to-DCE Data Rates for Each Mode
Mode Data Rate (bps) Affected Data
Data (V.34)
(transmit and receive)
2400–33,600
DTE-to-modem data rate
Fax 300–14,400
Voice 19,200–115,200
AT commands, playback and record modes
(varies according to compression type)
Table 3. DCE-to-ISP Data Rates for V.90 Mode
Mode Data Rate (bps) Affected Data
Data (V.90) transmit 4800–33,600
ISP-to-modem data rate
Data (V.90) receive 28,000–56,000
Data (V.92) transmit 24,000–48,000
Data (V.92) receive 28,000–56,000