Electrical – STM32: Is SWDIO pull-up required on the board

armstm32

One section of the STM32L431 manual (46.4 Pinout and debug port pins) says:

To avoid any uncontrolled I/O levels, the device embeds internal pull-ups and pull-downs on the JTAG input pins:

JTMS/SWDIO: internal pull-up

In another section (46.8 debug port), it says:

For SWDIO bidirectional management, the line must be pulled-up on the board (100 kOhm recommended by ARM).

Are both of these statements correct? How can this be?

People seem to be getting other ARMs working without an external pullup on SWDIO but my STM32 isn't working so I'm trying to narrow down the cause.

Best Answer

It is inconsistent. However the recommendation from ARM may be copied directly, as it does not assume that there would be internal pull-up on the SWDIO pin, but ST put an internal pull-up.

More than often it reads that the internal pull resistors on JTAG/SWD port eliminates the need for external resistors.

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Electronic – How to program STM32 Development Board

I have blinker example if you want to see

#include "stm32f10x_conf.h"

/* led connected to a gpio pin */
#define LED1_PIN    GPIO_Pin_0
#define LED1_PORT   GPIOB
#define LED2_PIN    GPIO_Pin_3
#define LED2_PORT   GPIOC
#define LED3_PIN    GPIO_Pin_0
#define LED3_PORT   GPIOA
#define LED4_PIN    GPIO_Pin_0
#define LED4_PORT   GPIOE


/* user functions */
void delay(unsigned long count);

int main()
{
    GPIO_InitTypeDef GPIO_InitStructure;



    /* enable clock on GPIOB peripheral */
    //RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);
    RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOB | RCC_APB2Periph_GPIOC | RCC_APB2Periph_GPIOE | RCC_APB2Periph_GPIOA, ENABLE);                          


    /* set pin output mode */
    GPIO_InitStructure.GPIO_Pin = LED1_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(LED1_PORT, &GPIO_InitStructure);
    //LED 2
    GPIO_InitStructure.GPIO_Pin = LED2_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(LED2_PORT, &GPIO_InitStructure);
    //LED 3
    GPIO_InitStructure.GPIO_Pin = LED3_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(LED3_PORT, &GPIO_InitStructure);
    //LED 4
    GPIO_InitStructure.GPIO_Pin = LED4_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(LED4_PORT, &GPIO_InitStructure);
    while(1)
    {
        GPIO_SetBits(LED1_PORT, LED1_PIN);  // set pin high
        delay(2000000);
        GPIO_ResetBits(LED1_PORT, LED1_PIN);    // set pin low
        delay(2000000);

        GPIO_SetBits(LED2_PORT, LED2_PIN);  // set pin high
        delay(2000000);
        GPIO_ResetBits(LED2_PORT, LED2_PIN);    // set pin low
        delay(2000000);

        GPIO_SetBits(LED3_PORT, LED3_PIN);  // set pin high
        delay(2000000);
        GPIO_ResetBits(LED3_PORT, LED3_PIN);    // set pin low
        delay(2000000);

        GPIO_SetBits(LED4_PORT, LED4_PIN);  // set pin high
        delay(2000000);
        GPIO_ResetBits(LED4_PORT, LED4_PIN);    // set pin low
        delay(2000000);
    }
    //return 0;
}



void delay(unsigned long count)
{
    while(count--);
}

Electronic – Setting the HSE clock frequency of an STM32

You have to supply the clock to the chip with either a crystal/ceramic resonator or other external clock signal.

The 4 to 26 MHz is not generated by the chip itself...

Best Answer

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Electronic – How to program STM32 Development Board

Electronic – Setting the HSE clock frequency of an STM32

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