Bouffalo Lab BL702 - UART Sampling Waveform

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BL702/704/706 Reference Manual

UART Clock

96M

Start

Stop

833

Baud rate˖115200 = 96M/833

Baud rate˖9600 = 96M/10000

10000

10000Sampling Time 5000

10000

Start

Fig. 10.3: UART sampling waveform

10.3.4 Transmitter

The transmitter contains a 128-byte transmit FIFO to store the data to be transmitted. Software can write TX FIFO

through APB bus, and can also move data into TX FIFO through DMA. When the transmit enable bit is set, the data

stored in the FIFO will be output from the TX pin. Software can choose to transfer data to TX FIFO through DMA or

APB bus. The software can check the status of the transmitter by querying the count value of the remaining available

space in the TX FIFO through the bit <TFICNT> of the register UART_FIFO_CONFIG_1. The FreeRun mode of the

transmitter is as follows: - If the FreeRun mode is not turned on, the sending behavior will be terminated and an

interrupt will be generated when the sent byte reaches the specified length. If you want to continue sending, you need

to turn off and then enable the send enable bit. - If the FreeRun mode is turned on, the transmitter will transmit when

there is data in the TX FIFO, and will not terminate because the transmitted byte reaches the specified length.

10.3.5 Receiver

The receiver contains a 128-byte receive FIFO to store the received data. The software can check the status of the

receiver by querying the count value of the available data in the RX FIFO through the bit <RFICNT> of the register

UART_FIFO_CONFIG_1. The lower 8 bits of the URX_RTO_TIMER register are used to set a receiving timeout

threshold. When the receiver does not receive data for more than this time value, it will trigger an interrupt. The

bits <DEGEN> and <DEGCNT> of the URX_CONFIG register are used to enable the deburring function and set the

threshold. It controls the filtering part before the UART sampling, and the UART will filter out the burrs whose width

is lower than the threshold in the waveform . Then send it to sampling.

BL702/704/706 Reference Manual 192/ 375

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