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NXP Semiconductors
QN902x
User Manual of QN902x
UM10996
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2018. All rights reserved.
User Manual
Rev 1.3
— 05 November 2018
91 of 128
Write buffer
read buffer
Shift register
Shift register
RX FSM
TX FSM
TXD
RXD
APB
interface
Transmitter
Receiver
Baud16
generator
Any UART bidirectional communication requires a minimum of two pins: Receive Data In
(RXD) and Transmit Data Out (TXD):
RXD
: Receive Data Input is the serial data input. Oversampling techniques are used for
data recovery by discriminating between valid incoming data and noise.
TXD
: Transmit Data Output is the serial data output. When the transmitter is disabled,
the output pin returns to its I/O port configuration. When the transmitter is enabled and
nothing is to be transmitted, the TX pin is at high level.
12.2.1
Baud Rate Generation
The baud rate generator generates
Baud16
clock signal by dividing down the input clock
UARTCLK
. The baud rate divisor (
BRD
) is a 22-bit number consisting of a 16-bit integer
and a 6-bit fractional part. The
Baud16
signal is then divided by 16 to give the baud rate:
Baud rate = Baud16/16 = (UARTCLK)/(16*BRD)
If we set the reference clock
(UARTCLK
) = 4MHz, then the generated baud rate error
can be calculated as follows:
GBRD = integer(UARTCLK/(16*BR)*64+0.5)/64
GBR = UARTCLK/(16*GBRD)
Error = (GBR
–
BR)/BR*100
where:
BR: Baud Rate
GBRD: Generated baud rate divider