Intel MD566X manual Originating Answering Resulting Connection Speed Modem

56K V.92 Data, Fax, and Voice Chipset

S-register S37 specifies the maximum data rate that can be attempted during a modem connection. If S37 is set to ‘0’, then the modem looks at the DTE rate to determine the maximum connection data rate. If the DTE data rate doesn’t match one of the <carrier> data rates, then the modem uses the next-fastest data rate.

The +MS command sets the modulation speeds in the MD566X chipsets; however, to set the modulation to either V.22 or Bell 212, the B0 or B1 command also must be sent. To set the modulation type to ITU-T V.22, send the B0 command; to set the modulation type to Bell 212, send B1. These commands can be entered before or after the +MS command. For example, to set the modulation to ITU-T V.22:

+MS = V22, 1, 1200, 1200; B0

It is important to remember that the ordering of commands is important in configuring the modem. For example, if the DTE 9600 bps data rate and the AT commands are issued in the following sequence, different connection rates result:

1. ATS37 = 0	2. AT+MS = V32B, 1, 0, 14400
AT+MS = V32B, 1, 0, 14400	ATS37 =	0
ATDT1234	ATDT1234
CONNECT 14400	CONNECT	9600

Table 3-3shows the resulting connection data rate when using non-default values. Because of impairments on the telephone line, the actual connection speeds may be lower than the speeds defined in this table.

For V.92, V.90 and V.34 modulations, the modem can receive data at a different data rate than the transmit data rate. All other modulation types besides V.23 and V.34 use the same data rate for the transmitter and receiver. Use ATW3 to see the modem’s actual receive and transmit data rates (the modem must be configured for ATV1 text response codes). Table 3-3shows examples of the resulting connection rate when non-default values are used.

Table 3-3. Resulting DCE-to-DCE Connection Rates with Non-Default Values

Originating	Answering	Resulting Connection Speed
Modem	Modem
+MS = V34, 1, 0, 0;	+MS = V32, 1, 0,	9600 bps: the originating modem is configured
		to attempt a maximum 28,800-bps connection,
the UART data rate	9600; the UART data
		but the answering modem is configured to
= 115,200 bps	rate = 14,400 bps
		attempt a maximum data rate of 9600 bps.
+MS = V34, 0,	+MS = V32B, 1, 0,	No connection: the originating modem is con-
28,800, 28,800;	9600; B1 and UART	figured to attempt only a 28,800 bps connec-
UART data rate =	data rate = 14,400	tion, but the answering modem is configured to
115,200 bps	bps	attempt a maximum data rate of 9600 bps.
N0, +MS = V32,		7200 bps: the originating modem is configured
	+MS = V34, 1, 0,0;	to attempt connection at 7200 bps or below.
1, 0, 9600; S37 =		The answering modem is configured to attempt
	UART data rate =
0; and UART data		a data rate of 9600 bps or below. The connec-
	9600 bps
rate = 7200 bps		tion takes place at 7200 bps, the highest
		speed supported by both modems.

Programmer’s Guide Intel Confidential 35