Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 20)

A N 9 3
20 Rev. 1.3
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.
Figure 2. Asychronous UART Serial Interface Timing Diagram
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.
Table 18. DTE Rates
Ideal DTE Rate (bps) Actual DTE Rate (bps) Approximate Error(%)
300 300
600 600
1200 1200
2400 2400
7200 7202 0.01
9600 9600
12000 12003 0.02
14400 14400
19200 19200
38400 38400
57600 57488 0.2
115200 115651 0.4
230400 228613 0.8
245760 245760
307200 307200
D1 D0 D2 D3 D4 D5 D6 D7
START
BIT
MARK
STOP
BIT
BIT TIMES
BIT SAMPLING
SPACE
D1 D0 D2 D3 D4 D5 D6 D7
START
BIT
MARK
STOP
BIT
BIT TIMES
BIT SAMPLING
SPACE
D8