Filter
Top Products
56K V.92 Data, Fax, and Voice Chipset
6 Intel Confidential Programmer’s Guide
1.1 V.92, V.90 and V.34 Data Modes
Intel® MD566X chipsets default to the ITU-T V.90 or V.92 data transmission mode depending on
the firmware version. The V.90/V.92 mode allows receive data rates of up to 56 kbps over the
PSTN (public switched telephone network) only in connections with equipment-compatible ISPs
(Internet Service Providers); however, FCC regulations limit receive speeds to 53,333 kbps due to
excessive power demands at higher speeds. In modem-to-modem connections V.90/V.92 mode falls
back to the V.34 mode in both the transmit and receive directions.
1.2 Modem Connection Overview
The DCE (modem) operates in one of two states: command or online. In each state, both data and
commands (including DCE responses) are transferred through the UART THR (Transmit Holding
register) and the RBR (Receiver Buffer register).
The modem defaults to the command state. In the command state, the DTE (host) communicates to
the modem through AT commands and S-registers. AT commands are character strings that help
guide modem operation. S-registers are internal modem registers that the DTE can access. The S-
registers contain modem status and configuration information. Many of the AT commands
indirectly affect the contents of the S-registers. The MD566X’s AT command set and S-registers
are divided into the following modes: Group 3 fax, data, V.42/MNP, voice. See Chapter 2 on page 8
for command table summaries.
All command lines sent to the modem, except for A/, must be preceded by an ‘AT’ (which stands
for ‘attention’) and terminated by the contents of S-register S3 (typically a carriage return <CR>).
The ‘AT’ prompts the modem to receive a command line from the DTE. A <CR> informs the
modem that the entire command string has been transmitted and that the modem should start
processing all the commands within the command line.
A command line may include one or more AT commands that may or may not be separated by a
space. AT commands may be either upper- or lower-case characters, but all characters for a given
command must use the same case. If there are multiple commands in a line, a semicolon (;) must be
placed after each fax or voice command. The modem can be configured to send back (echo) to the
DTE any data that the DTE sends to the modem (while in command state only). The last command
may be repeated by typing A/ without using a carriage return. Each command line may include up
to 80 characters and spaces.
Examples of AT command strings:
ATS1?<CR>
A/
AT &C1 &D2 +FCLASS=? <CR>
AT &C1 &D2 +FCLASS=?; S0=1 <CR>
The modem provides status information to the DTE in the form of response codes. These response
codes can be expressed in text or numeric form. The supported response codes for V.90 mode are
provided in Table 2-10 on page 21 and V.34 response codes are included in Table 2-11 on page 22.