Hello,I have defined the system as The APB1 CLK is defined by 45MHz as shown bellow.
The Usart2 periphery is on the APB1 bus.
By the full code attached bellow the USART2 and gpio settings are as following by the printscreen from the reference manual.
The OSPEEDR is set to be fast.
USART2->CR1|=(1<<13);
USART2->CR1&=~(1UL<<12);
By the USART2 CR1 register bit 12 the data packet is 8 bit long.
USART2->BRR=(7<<0)|(24<<4);
The most critical thing is BRR i put 7 in location 0 and 24 at location 4 as shown in the printscreen bellow.
My USART CLK is 45MHz which is divided by 16*24.7
45000000/(16*24.7)=113866
In reality i get the following Scope waveform which is not the calculated frequency.
the distance of a single bit as you can see between the cursors is 2.4uS
Where did i get wrong why i got such low frequency?
The full code is shown bellow.
Thanks.
* The system Clock is configured as follow :
* System Clock source = PLL (HSE)
* SYSCLK(Hz) = 180000000
* HCLK(Hz) = 180000000
* AHB Prescaler = 1
* APB1 Prescaler = 4
* APB2 Prescaler = 2
* HSE Frequency(Hz) = 8000000
* PLL_M = 4
* PLL_N = 180
* PLL_P = 2
* VDD(V) = 3.3
* Main regulator output voltage = Scale1 mode
* Flash Latency(WS) = 5
#include "rcc_config.h"
void uart2config(void);
void uart2_sendchar(uint8_t );
void uart2config(void)
{
RCC->APB1ENR|=RCC_APB1ENR_USART2EN;
RCC->AHB1ENR|=RCC_AHB1ENR_GPIOAEN;
//why in EFR32 we haveoutput but in stm32 we have alternate function for GPIO
//GPIO speed i did not use in EFR32 what is speed in GPIO
GPIOA->MODER|=(1UL<<7);//pin A3
GPIOA->MODER&=~(1UL<<6);//pin A3
GPIOA->MODER|=(1UL<<5);//pin A2
GPIOA->MODER&=~(1UL<<4);//pin A2
GPIOA->OSPEEDR|=(1UL<<7);//pin A3
GPIOA->OSPEEDR&=~(1UL<<6);//pin A3
GPIOA->OSPEEDR|=(1UL<<5);//pin A2
GPIOA->OSPEEDR&=~(1UL<<4);//pin A2
//8.4.9 285 why we need
GPIOA->AFR[0]|=(7<<8);
GPIOA->AFR[0]|=(7<<12);
USART2->CR1|=(1<<13);
USART2->CR1&=~(1UL<<12);
USART2->BRR=(7<<0)|(24<<4);
USART2->CR1|=(1<<2);
USART2->CR1|=(1<<3);
}
//bitwise and
void uart2_sendchar(uint8_t c)
{
USART2->DR=c;
while(!(USART2->SR&(1<<6)));
}
int main(void)
{
uart2config();
while(1)
{
uart2_sendchar(0b10101000);
delay(10000);
}
}
