AN4157 Datasheet, PDF (17/24 Pages) STMicroelectronics – STM32F3DISCOVERY peripheral firmware examples

AN4157
Peripheral firmware examples description
Note:
TIM1 is configured to generate the reference signal used by TIM8 on Channel1:
● TIM1 generates a PWM signal with a frequency equal to 1.4560 kHz.
● TIM1 is used as master for TIM8: TIM1 update event resets TIM8 counter to
synchronize the reference signal (TIM1_CH1) and the shifted signal (TIM8_CH2).
TIM1 and TIM8 input clock (TIM18CLK) is set to APB2 clock (PCLK2). TIM1 and TIM8
signals are at frequency of (SystemCoreClock / (Period + 1)).
TIM8 generates a signal with the following characteristics:
Pulse length = (TIM8_CCR1 + TIM8_CCR2) / TIM8_CLK
Phase shift = TIM8_CCR1/TIM8_CLK
where TIM8_CLK = (SystemCoreClock / (Period + 1)), as the prescaler is equal to zero.
Connect the following pins to an oscilloscope to monitor the different waveforms:
● PA08 (TIM1_CH1)
● PB08 (TIM8_CH2)
● PB06 (TIM8_CH1)
The shift is measured using the TIM1_CH1 as reference signal.
3.20
3.20.1
3.20.2
TIM combined example
Purpose
This example provides a short description of how to configure the TIM1 peripheral to
generate 3 PWM combined signals with TIM1 Channel5.
Description
The TIM1 input clock (TIM1CLK) with prescaler 0 is set to APB2 clock (PCLK2), which is
equal to system clock (SystemCoreClock).
SystemCoreClock is set to 72 MHz for STM32F30x or STM32F31x devices.
The objective is to generate 3 combined PWM signal at 8.78 kHz (in center aligned mode):
TIM1_Period = (SystemCoreClock / (8.78*2)) - 1
● The channel 1 duty cycle is set to 50%
● The channel 2 duty cycle is set to 37.5%
● The channel 3 duty cycle is set to 25%
The Timer pulse is calculated as follows:
ChannelxPulse = DutyCycle * (TIM1_Period - 1) / 100
The channel 5 is used in PWM2 mode with duty cycle set to 6.22%
The 3 resulting signals are made of an AND logical combination of two reference PWMs:
● Channel 1 and Channel 5
● Channel 2 and Channel 5
● Channel 3 and Channel 5
Doc ID 023629 Rev 1
17/24