Table 47. Counting Direction Versus Encoder Signals; Figure 125. Example Of Counter Operation In Encoder Interface Mode - STMicroelectronics STM32F05 series Reference Manual

General-purpose timers (TIM2 and TIM3)
Table 47.
Active edge
Counting on
TI1 only
Counting on
TI2 only
Counting on
TI1 and TI2
An external incremental encoder can be connected directly to the MCU without external
interface logic. However, comparators are normally be used to convert the encoder's
differential outputs to digital signals. This greatly increases noise immunity. The third
encoder output which indicate the mechanical zero position, may be connected to an
external interrupt input and trigger a counter reset.
Figure 125
direction control. It also shows how input jitter is compensated where both edges are
selected. This might occur if the sensor is positioned near to one of the switching points. For
this example we assume that the configuration is the following:
●
CC1S= 01 (TIMx_CCMR1 register, TI1FP1 mapped on TI1)
●
CC2S= 01 (TIMx_CCMR2 register, TI2FP2 mapped on TI2)
●
CC1P=0, CC1NP = '0' (TIMx_CCER register, TI1FP1 noninverted, TI1FP1=TI1)
●
CC2P=0, CC2NP = '0' (TIMx_CCER register, TI2FP2 noninverted, TI2FP2=TI2)
●
SMS= 011 (TIMx_SMCR register, both inputs are active on both rising and falling
edges)
●
CEN= 1 (TIMx_CR1 register, Counter is enabled)

Figure 125. Example of counter operation in encoder interface mode

Counter
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Counting direction versus encoder signals
Level on opposite
signal (TI1FP1 for
TI2, TI2FP2 for TI1)
High
Low
High
Low
High
Low
gives an example of counter operation, showing count signal generation and
forward jitter
TI1
TI2
up
Doc ID 018940 Rev 1
TI1FP1 signal
Rising Falling
Down Up
Up Down
No Count No Count
No Count No Count
Down Up
Up Down
backward jitter
down
RM0091
TI2FP2 signal
Rising Falling
No Count No Count
No Count No Count
Up Down
Down Up
Up Down
Down Up
forward
up