STM32F407 Discovery board and TLC5947

[VYada.3]

Hi

I'm new to using STM Microcontrollers and I have the Discovery board as my development board, I have used Arduino religiously and thought I should learn something new.

I have learnt how to modify data registers, for example, turn the 4 LEDs on and off, also get an input from the push button to get the Leds to turn on.

Am now looking at PWM, which I did get to work. I had a previous project which uses these TLC5947 to turn some LEDs on, I used Arduino and it worked fine, since it used PWM I thought I could practice with these. Unfortunately, trying to get it to work with the discovery board isn't working out the way that I want and was wondering if someone can help me.

I know the Arduino has a 16Mhz clock and PWM frequency is 490hz and I know the discovery board is way higher. I just generally don't know where to begin

adfruit has a libaray file which modifys the pwm high and low using the code below

void Adafruit_TLC5947::write() {
  digitalWrite(_lat, LOW);
  // 24 channels per TLC5974
  for (int16_t c = 24 * numdrivers - 1; c >= 0; c--) {
    // 12 bits per channel, send MSB first
    for (int8_t b = 11; b >= 0; b--) {
      digitalWrite(_clk, LOW);
 
      if (pwmbuffer[c] & (1 << b))
        digitalWrite(_dat, HIGH);
      else
        digitalWrite(_dat, LOW);
 
      digitalWrite(_clk, HIGH);
    }
  }
  digitalWrite(_clk, LOW);
 
  digitalWrite(_lat, HIGH);
  digitalWrite(_lat, LOW);
}

Of course, I thought that I could just use the pins on the dsicvoery board to do the same thing, high and low however that doesn't work, don't even know why I thought it would. It uses the Arduino PWM pins and this is where I was stuck.

I even thought maybe logic level shifters would work, but that didn't work either I even used delays, however nothing.

I know the discovery board can use 16Mhz (however if I do that I fell like I should just stick with the Arduino) by modifying the HSI but not 100% sure how to go about that, I would even need to change the pre scale value to make the frequency to 490Hz and change the counter period to 255, again not 100% sure how to go about that I have tried and I think I'm doing something wrong.

any help would be great or am i just wasting my time and to just stick with arduino

Thank you

[Tesla DeLorean]

The code you show just drives pins high and low, it doesn't use PWM modes.

​On the STM32 you can define the frequency and duty of TIM pins significantly more precisely and broadly than the Arduino implementation.​

[Tesla DeLorean]

You might need delays between GPIO pin transitions here. Presume you haven't checked the timing requirements and don't have a scope.​

[waclawek.jan]

Which STM32?

What hardware?

The code you've presented looks awful lot like SPI. You can transmit similar sequence also using Synchronous mode of USART.

JW

[VYada.3]

Hi

i thought since it is just high and low that it would work just by toggling the PD pins

below is what i tried with the delays

void write(void){
	*pPortDOutReg &= ~(1 << 12);
		for (int16_t c = 24 * 1 - 1; c >= 0; c--) {
			 for (int8_t b = 11; b >= 0; b--) {
				   *pPortDOutReg &= ~(1 << 14);
			      if (pwmbuffer[c] & (1 << b)){
			    	  *pPortDOutReg |= (1 << 15);
			      }else{
			    	  *pPortDOutReg &= ~(1 << 15); 
			         *pPortDOutReg |= (1 << 14);
			      }
			      delay();
			    }
			 	delay2();
		}
		*pPortDOutReg &= ~(1 << 14);
		*pPortDOutReg |= (1 << 12);
		*pPortDOutReg &= ~(1 << 12);
		printf("----END---- \n");
}
 
void delay(void){
	for(uint32_t i=0; i < 7500; i++);
}
 
void delay2(void){
	for(uint32_t i=0; i < 225; i++);
}

I used a scope to measure against the Arduino, when I initialize delay () where it is I have to set the delay to 7500, so PD15 matches what come out of the arduino. However, when I italize delay2 () for 255 where it is PD14 matches, however it screws up the delay for PD15 and vice versa

[VYada.3]

Hi

im using STM32F407G-DISC board connected to this board

https://www.adafruit.com/product/1429

i just checked and it looks like it is an SPI interface, of course since im learning would you know a good tutorial on SPI with the discovery board as i have no idea where to start

Thank you

[VYada.3]

Hi

it says the TLC5947 has to have 15Mhz SCLK im using SPI1 which i belive is connected to APB1 periphal clock which is at 42Mhz i can prescale the baud rate but by the factor of 2 which means i can not get it to 15Mhz. if i divide by 2 i get 21 is i divide by 4 i get 10.

how woulds i go about this

Thank you

[Peter BENSCH]

The TLC5947 can be used in cascade, i.e. several in a row, up to max. 15MHz, up to 30MHz if it is only one. In both cases it is the maximum clock frequency, not the exact one.

[VYada.3]

ok im a complete idiot all i had to do was lower the APB1 periphal clock by a factor of 8 and just use the PD pins connected to the on board LEDs as the _clk, _dat and _lat. thank you @Peter BENSCH​ for reminding me that those are the max MHz needed not the exact ones