DocID022500 Rev 4

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AN4013

Advanced features for motor control

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Figure 8. Position at X2 resolution

Note:

The counter in case of resolution X2 can also be incremented on the TI1 edge.

In STM32 timer encoder interface mode, the encoder mode3 corresponds to resolution X4.

In this mode, the counter counts up/down on both TI1 and TI2 edges.

The resolution X2 is selected when encoder mode 1 or mode 2 is selected, that is, the

counter counts up/down on TI2 edge depending on the TI1 level, or the counter counts

up/down on TI1 edge depending on TI2 level.

How to use the encoder interface

An external incremental encoder can be connected directly to the MCU without external

interface logic. The third encoder output (index) which indicates the mechanical zero

position, may be connected to an external interrupt input and trigger a counter reset.

The output signal of the incremental encoder is filtered by the STM32 timer input filter block

to reject all noise sources that typically occur in motor systems. This filter is used as

described in Section 2.3: Timer input capture mode.

TIM configuration in encoder mode

1.

Select and configure the timer input:



Input selection:

–

TI1 connected to TI1FP1 CC1S='01' in CCMR1 register

–

TI2 connected to TI2FP2 CC2S='01' in CCMR1 register



Input polarity:

–

CC1P='0' and CC1NP='0'(CCER register, TI1FP1 non-inverted, TI1FP1=TI1).

–

CC2P='0' and CC2NP='0'(CCER register, TI1FP2 non-inverted, TI1FP2= TI2).

2.

Select the encoder mode



Encoder mode1 (resolution X2 on TI2): SMS=’001’ in SMCR register.



Encoder mode2 (resolution X2 on TI1): SMS=’010' in SMCR register.



Encoder mode3 (resolution X4 on TI1 and TI2): SMS=’011’ in SMCR register.

3.

Enable the timer counter



Set the counter enable bit, CEN='1' in CR1 register.