SI2457-D-FS Silicon Laboratories Inc, SI2457-D-FS Datasheet - Page 20

• Manufacturer Part Number: SI2457-D-FS
• Description: IC ISOMODEM SYSTEM-SIDE 16SOIC
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2457-D-FS

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

AN93
The UART interface synchronizes on the start bits of incoming characters and samples the data bit field and stop
bits. The interface is designed to accommodate character lengths of 8, 9, 10, and 11 bits giving data fields of 6, 7,
8, or 9 bits. Data width can be set to 6, 7, or 8 bits with the AT\Bn command. Parity can be set to odd, even, mark,
or space by the AT\Pn command in conjunction with AT\B2 or AT\B5. Other AT\Bn settings have no parity.
2.2.3.2. Autobaud
When set in UART interface mode, the ISOmodem includes an automatic baud rate detection feature that allows
the host to start transmitting data at any standard DTE rate from 300 bps to 307.2 kbps. This feature is enabled by
default. When autobaud is enabled, it continually adjusts the baud rate, and the ISOmodem always echoes result
codes at the same baud rate as the most recently received character from the host. Autobaud can be turned off
using AT commands \T0 through \T15, and \T17. Host software should disable autobaud operation once the DTE
rate has been established. This prevents transients on TXD to cause inadvertent baud rate changes.
Autobaud is off when dialing, answering, and in data mode. When autobaud mode is off, the baud rate is set to the
most recently-active baud rate prior to entering one of these states. When autobaud mode is on, autoparity is
performed when either “at” or “AT” is detected. Autoparity detects the formats listed in Table 19.
20
SPACE
SPACE
MARK
MARK
BIT TIMES
BIT TIMES
BIT SAMPLING
BIT SAMPLING
START
START
BIT
BIT
Ideal DTE Rate (bps)
Figure 2. Asychronous UART Serial Interface Timing Diagram
230400
245760
307200
115200
D0
12000
14400
19200
38400
57600
1200
2400
7200
9600
300
600
D0
D1
D1
D2
Table 18. DTE Rates
Actual DTE Rate (bps)
D2
D3
228613
245760
307200
Rev. 1.3
115651
12003
14400
19200
38400
57488
1200
2400
7202
9600
300
600
D3
D4
D4
D5
Approximate Error(%)
D5
D6
0.01
0.02
0.2
0.4
0.8
D6
D7
D7
D8
STOP
STOP
BIT
BIT