Public Version
UART/IrDA/CIR Functional Description
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19.4.4.1.3.4 Autobauding Modes
In autobauding mode, the UART can extract transfer characteristics (speed, length, and parity) from an AT
command (ASCII code). These characteristics are used to receive data after an "at" (AT) and to send
data.
The valid AT commands follow:
AT
DATA
<CR>
at
DATA
<CR>
A/
a/
A line break during the acquisition of the sequence AT is not recognized, and echo functionality is not
implemented in hardware.
A/ and a/ are not used to extract characteristics, but they must be recognized because of their special
meaning. Either A/ or a/ is used to instruct the software to repeat the last received AT command;
therefore, an a/ always follows an AT, and transfer characteristics are not expected to change between an
AT and an a/.
When a valid AT is received, AT and all subsequent data, including the final <CR> (0x0D), are saved to
RX FIFO. The autobaud state-machine waits for the next valid AT command. If an a/ (A/) is received, the
a/ (A/) is saved into RX FIFO and the state-machine waits for the next valid AT command.
On the first successful detection of the baud rate, the UART activates an interrupt to signify that the AT
(upper or lower case) sequence is detected. The UARTi.
register reflects the correct settings
for the baud rate detected. The interrupt activity can continue in this fashion when a subsequent character
is received. Therefore, it is recommended that the software enable the RHR interrupt when using the
autobaud mode.
The following settings are detected in autobaud mode with a module clock of 48 MHz:
•
Speed: 115.2k baud, 57.6k baud, 38.4k baud, 28.8k baud, 19.2k baud, 14.4k baud, 9.6k baud, 4.8k
baud, 2.4k baud, or 1.2k baud
•
Length: 7 or 8 bits
•
Parity: Odd, even, or space
NOTE:
The combination of 7-bit cha space parity is not supported.
Autobauding mode is selected when the UARTi.
[2:0] MODE_SELECT field is set to 0x2. In
the UART autobauding mode, UARTi.
, UARTi.
[5:0] settings are
not used; instead,
is updated with the configuration detected by the autobauding logic.
Autobauding Status Register Use
This register is used to set up transmission according to the characteristics of the previous reception
instead of the UARTi.
, UARTi.
registers when the UART is in
autobauding mode.
To reset the autobauding hardware (to start a new AT detection) or to set the UART in standard mode (no
autobaud), the UARTi.
[2:0] MODE_ SELECT field must be set to reset state (0x7) and then to
the UART in autobauding mode (0x2) or to the UART in standard mode (0x0).
Use limitation:
•
Only 7- and 8-bit characters (5- and 6-bit not supported)
•
7-bit character with space parity not supported
•
Baud rate between 1,200 and 115,200 bps (10 possibilities)
2908
UART/IrDA/CIR
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated
