PM0222 datasheet(23/33 Pages) STMICROELECTRONICS

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PM0222

UART

All UART registers are described in a structure defined in the Brain header file (.h) provided

by STMicroelectronics.

Brain has one UART available at the following address in the memory map:

UART APB base address: 0xA200_0000

9.1

FIFO management

The transmit and receive paths are buffered with internal FIFO memory enabling up to 32

bytes to be stored independently in both transmit and receive modes.

9.2

Baud rate calculation example

To define the UART baud rate generation there are two registers to configure, UARTIBRD

and UARTFBRD. Those two registers contain respectively the decimal and the fractional

part of the BAUDDIV data. We can calculate this data using the following formula:

BAUDDIV = ( FUARTCLK / (16 x Baud rate) )

With:



FUARTCLK is the UART reference clock frequency. It corresponds to the processor

clock divided by a programmable value from 2 to 127 (see Brain reference manual,

Clock and reset management unit chapter for more details).



Baud rate is the Baud rate required by the user’s program

The UARTFBRD field value is calculated as follows:

integer(fractional part of BAUDDIV * 64 + 0.5)

Example: calculating the divisor value

If the requested baud rate is 230400 and FUARTCLK = 4 MHz then:

BAUDDIV = ( 4 x 106 ) / ( 16 x 230400 ) = 1.085

This means that the decimal part BDRI = 1 and the fractional part BDRF = 0.085.

UART->UARTIBRD = 0x1; // configure the integer part of BAUDDIV

UART->UARTFBRD = 0x5; // configure the fractional part of BAUDDIV

See Brain reference manual, UART chapter, UARTFBRD register description for more

details.

PM0222 Datenblatt(PDF) 23 Page - STMicroelectronics