Functional Description
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19.3.8.1.3.4 Autobauding Modes
In autobauding mode, the UART can extract transfer characteristics (speed, length, and parity) from an
"at" (AT) command (ASCII code). These characteristics are used to receive data after an AT and to send
data.
The following AT commands are valid:
AT DATA <CR>
at DATA <CR>
A/
a/
A line break during the acquisition of the sequence AT is not recognized, and an echo function is not
implemented in hardware.
A/ and a/ are not used to extract characteristics, but they must be recognized because of their special
meaning. 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
the RX FIFO. The autobaud state-machine waits for the next valid AT command. If an a/ (A/) is received,
the a/ (A/) is saved in the 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.UART_UASR register reflects the correct settings
for the baud rate detected. 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
– 1.2K baud
• Length: 7 or 8 bits
• Parity: Odd, even, or space
NOTE: The combination of 7-bit character plus space parity is not supported.
Autobauding mode is selected when the UARTi.UART_MDR1[2:0] MODE_SELECT bit field is set to 0x2.
In UART autobauding mode, UARTi.UART_DLL, UARTi.UART_DLH, and UARTi.UART_LCR[5:0] bit field
settings are not used; instead, UART_UASR is updated with the configuration detected by the
autobauding logic.
UART_UASR Autobauding Status Register Use
This register is used to set up transmission according to the characteristics of the previous reception
instead of the UARTi.UART_LCR, UARTi.UART_DLL, and UARTi.UART_DLH registers when the UART is
in autobauding mode.
3478
Universal Asynchronous Receiver/Transmitter (UART) SPRUH73H–October 2011–Revised April 2013
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