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SI3010-F-FS

V.22BIS ISOMODEM® WITH INTEGRATED GLOBAL DAA

Silicon Laboratories 

Si2401

4.1. Serial Interface

The Si2401 has a universal asynchronous receiver/

transmitter (UART) serial interface compatible with

standard microcontroller serial interfaces. After powerup

or reset, the speed of the serial (Data Terminal

Equipment—DTE) interface is set by default to

2400 bps with the 8-bit, no parity, and one-stop bit (8N1)

format described below.

The serial interface DTE rate can be modified by writing

SE0[2:0] (SD) with the value corresponding to the

desired DTE rate. (See Table 8.) This is accomplished

with the command, ATSE0=xx, where xx is the

hexadecimal value of the SE0 register.

Table 8. DTE Rates

Table 9. Modem Configuration Examples

(S07[7] (HDEN) = 0, S07[6] (BD) = 0)

Modem Protocol

V.22bis

V.22

V.21

Bell 212A

Bell 103

V.23 (1200 tx, 75 rx)

V.23 (75 tx, 1200 rx)

V.23 (600 tx, 75 rx)

V.23 (75 tx, 600 rx)

Register S07 Values

0x06

0x02

0x03

0x00

0x01

0x16

0x26

0x10

0x20

DTE Rate (bps)

300

1200

2400

9600

19200

38400

115200

307200

SE0[2:0] (SD)

000

001

010

011

100

101

110

111

Immediately after the ATSE0=xx string is sent, the host

UART must be reprogrammed to the new DTE rate in

order to communicate with the Si2401.

The carriage return character following the ATSE0=xx

string must be sent at the new DTE rate to observe the

“O” response code. See Table 12 on page 24 for the

response code summary.

4.2. Configurations and Data Rates

The Si2401 can be configured to any of the Bell and

CCITT operation modes listed in Table 9. When

configured for V.22bis, the modem connects at

1200 bps if the far end modem is configured for V.22.

This device also supports SIA and other protocols for

the security industry. Table 7 provides the modulation

method, carrier frequencies, data rate, baud rate, and

notes on standard compliance for each modem

configuration of the Si2401. Table 9 shows example

register settings (S07) for some of the modem

configurations.

As shown in Figure 3, 8-bit and 9-bit data modes refer to

the DTE format over the UART. Line data formats are

configured through registers S07 (MF1) and S15 (MLC).

If the number of bits specified by the format differs from

the number of bits specified by the DCE data

communications equipment or line (DTE) format, the

MSBs are either dropped or bit-stuffed, as appropriate.

For example, if the DTE format is 9 data bits (9N1), and

the line data format is 8 data bits (8N1), the MSB from

the DTE is dropped as the 9-bit word is passed from the

DTE side to the DCE (line) side. In this case, the

dropped ninth bit can then be used as an escape

mechanism. However, if the DTE format is 8N1, and the

line data format is 9N1, an MSB equal to 0 is added to

the 8-bit word as it is passed from the DTE side to the

DCE side.

The Si2401 UART does not continuously check for stop

bits on the incoming digital data. Therefore, if the TXD

pin is not high, the RXD pin may echo meaningless

characters to the host UART. This requires the host

UART to flush its receiver FIFO upon initialization.

TXD

RXD

Si2401 Si3010

RJ11

DTE Interface

Data Rate: SE0[2:0] (SD)

Data Format: SE0[3] (ND)

DCE (Line) Interface

Data Rate: S07 (MF1)

Data Format: S15 (MLC)

Figure 3. Link and Line Data Formats

Rev. 1.0

13

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