STM32F107VC/Using MCBQVGA-TS-Display-v12
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Backlight illumination adjust
The signal BL_control[1] turns on the Backlight LED's controlled by the STLD40D[2] IC on the display. To control the illuminace of the LED's its necessary to turn the LED's off and on using Pulse-Width-Modulation (PWM).
Keil MCBSTM32C board
On the Keil MCBSTM32C board the BL_control signal is connected to PB0 (Port B bit 0).
- Looking in the Reference Maual on page 173 section 9.3.7 table 44 it's seen that Timer 3 Channel 3 has an alternate function on PB0.
- To see Timer 3's possibilities on PB0 look on page 161 section 9.1.11 table 23 it's seen that timer 3 can use a GPIO pin as Output Compare Channel X when the pin is configured as Alternate Function Push-Pull.
- To set PB0 as Alternate Function Push-Pull - See the GPIOx_CRL register on page 166.
- To configure Timer 3 as continues PWM output timer see Page 371 section 15.3.9
Example code
Still experimental and missing documentation
- Note
- To change Pulse Width change the value of TIM3->CCR3
/*
Example 2:
==========
Using timer 3 to Dim the Backlight in Display
Mode : Continues PWM mode to PB0. Section 15.3.9 page 370
For details see: http://mars.tekkom.dk/mediawiki/index.php/STM32F107VC/Using_MCBQVGA-TS-Display-v12
Caveats: Assumes TIMxCLK = 72 MHz (See RCC - Reset And Clock Control)
*/
void tim3init( void ) {
GPIOB->CRL |= 0xa; // Set PB0 as Alternate function Push-Pull
RCC->APB1ENR |= 2; //Enable timer 3 clock (RCC->APB1ENR bit 1 = 1)
TIM3->PSC = 72; // Prescaler: With timer 3 input clock 72 Mhz divide by 72 to 1 Mhz
TIM3->ARR = 1000; // Auto Reload Register set to 1000 divide 1Mhz/1000 = 1 Khz
TIM3->CCR3 = 100; //Compare Register for channel 3
TIM3->CCMR2 |= 7 << 4; //PWM mode 1
TIM3->CCMR2 |= 1 << 3;
TIM3->EGR |= 1; //Update generate
TIM3->CCER |= 1<<8; //Polarity
TIM3->CCER |= 1<<9;
TIM3->CR1 |= 1;
}
/* Change Display Backlight Intensity
input: 0 - 17 ( 0 = 0% backlight (All dark) to 17 = 100% backlight (Brigth)
Caveats: No errorcontrol
When 0 the timer should be turned off and the backlight turned off (PB0=0)
when 17 the timer should be turned off and the backlight turned on (PB0=1)
*/
void backlight( int intensity ) {
int disvalarr[] = {0,5,10,15,25,35,50,65,80,100,120,150,200,300,400,600,800,1000};
TIM3->CCR3 = disvalarr[intensity];
}
Links
- MCBSTM32C Display Schematics (Loads PDF)
- AM-240320LDTNQW TFT-LCD Display module with Touch Panel (Loads PDF)
- SPFD5408B 720 channel driver for TFT-LCD Display (Loads PDF)
- STMPE811 Touch Screen Controller
- STLD40D White LED power supply for large display backlight (Loads PDF)