I use to stm32f302 to measure the external encoder signal. There is no problem at low speed, but it will not work when the pulse width is reduced to about 11us. I want to know what is the limit pulse width (minimum) when TIM is set to encoder mode.
Pulse width as shown：
The initialization code is as：
void encoder_pin_init(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
RCC_AHBPeriphClockCmd( RCC_AHBPeriph_GPIOB, ENABLE);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7 | GPIO_Pin_6;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init( GPIOB, &GPIO_InitStructure );
GPIO_PinAFConfig(GPIOB, GPIO_PinSource6, GPIO_AF_2);
GPIO_PinAFConfig(GPIOB, GPIO_PinSource7, GPIO_AF_2);
}
void encoder_timer_init(void)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
/* TIM_ICInitTypeDef TIM_ICInitStructure;
*/
RCC_APB1PeriphClockCmd( RCC_APB1Periph_TIM4, ENABLE );
TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
TIM_DeInit(TIM4);
TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);
TIM_TimeBaseStructure.TIM_Period =0xffffu;
TIM_TimeBaseStructure.TIM_Prescaler =0u;
TIM_TimeBaseStructure.TIM_ClockDivision = 0u;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);
TIM_EncoderInterfaceConfig( TIM4,
TIM_EncoderMode_TI1,
TIM_ICPolarity_Rising,
TIM_ICPolarity_Rising );
/* TIM_ICStructInit(&TIM_ICInitStructure);
TIM_ICInitStructure.TIM_ICFilter = 6;
TIM_ICInit(TIM4, &TIM_ICInitStructure);
TIM_ICInitStructure.TIM_Channel = TIM_Channel_2;
TIM_ICInit(TIM4, &TIM_ICInitStructure); */
TIM_Cmd(TIM4, ENABLE);
}
So here is an improved version thanks to the comments by @Community member
It counts the edges on TIM4_CH2, counting direction is determined by CH1 XOR CH3. Connect the direction signal to either CH1 or CH3, and pull down the other pin to GND. Leaving the unused timer input unconfigured, i.e. no pin assigned should work too, but this is not officially documented.
TIM4->CR2 = TIM_CR2_TI1S; // TIMx_CH1, CH2 and CH3 pins are connected to the TI1 input (XOR combination)
TIM4->SMCR = TIM_SMCR_SMS_1; // 0b0010: Encoder mode 2 - Counter counts up/down on TI2FP2 edge depending on TI1FP1 level.
TIM4->CCMR1 =
(0b01 << TIM_CCMR1_CC1S_Pos) | // 0b01: CC1 channel is configured as input, IC1 is mapped on TI1
(0b0010 << TIM_CCMR1_IC1F_Pos) | // 0b0010: fSAMPLING=***_INT, N=4
(0b01 << TIM_CCMR1_CC2S_Pos) | // 0b01: CC2 channel is configured as input, IC2 is mapped on TI2
(0b0011 << TIM_CCMR1_IC2F_Pos) | // 0b0011: fSAMPLING=***_INT, N=8
0;
TIM4->CR1 = TIM_CR1_CEN; // enable counterThe timer is in encoder mode 2, counting the edges on TI2FP2, and using TI1FP1 (which is actually CH1^CH2^CH3) as the direction signal. Channels 1 and 2 are configured as inputs connected to TI1FP1 and TI2FP2 respectively. Look up the General-purpose timer block diagram in the reference manual if this makes little sense to you so far. There is a 4 cycles digital filter on TI1, and 8 cycles on TI2 to ensure that a transition on CH2 reaches TI1FP1 first.
Let's suppose all inputs are initially low, then there is a rising edge on CH2. The input filter duration on TI1 is shorter, so the "opposite signal" is rising first, followed by TI2FP2 rising, resulting in the counter going up. Then there is a falling edge on CH2, "opposite signal" is already low when TI2FP2 is falling, causing the counter going up again. When CH1^CH3 is high, TI1 is the opposite of CH2, so the counter counts down on both the rising and the falling edge of CH2.
Some filtering is apparently necessary on TI1, the counter is sporadically changing when I remove the TI1 filter (IC1F) and change the direction repeatedly. It might be the result of my not too sophisticated test setup, which means touching dangling jumper wires to ground and using the internal pullups.
