EM357-RTR datasheet(141/240 Pages) ETC2

141 / 240 page

EM351 / EM357

Table 9-3. Counting Direction versus Encoder Signals

TI1FP1 Signal

TI2FP2 Signal

Active Edges

Level on

Opposite Signal

(TI1FP1 for TI2,

TI2FP2 for TI1)

Rising

Falling

Rising

Falling

High

Down

No Count

Counting on TI1

only

Low

Down

No Count

High

No Count

Down

Counting on TI2

only

Low

No Count

Down

High

Down

Counting on TI1

and TI2

Low

Down

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

However, comparators are normally used to convert an encoder’s differential outputs to digital signals, and

this greatly increases noise immunity. If a third encoder output indicates the mechanical zero (or index)

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

Figure 9-25 gives an example of counter operation, showing count signal generation and direction control. It

also shows how input jitter is compensated for when both inputs are used for counting. This might occur if the

sensor is positioned near one of the switching points. This example assumes the following configuration:

TIM_CC1S = 01 (TIMx_CCMR1 register, IC1FP1 mapped on TI1).

TIM_CC2S = 01 (TIMx_CCMR2 register, IC2FP2 mapped on TI2).

TIM_CC1P = 0 (TIMx_CCER register, IC1FP1 non-inverted, IC1FP1 = TI1).

TIM_CC2P = 0 (TIMx_CCER register, IC2FP2 non-inverted, IC2FP2 = TI2).

TIM_SMS = 011 (TIMx_SMCR register, both inputs are active on both rising and falling edges).

TIM_CEN = 1 (TIMx_CR1 register, counter is enabled).

Figure 9-25. Example of Counter Operation in Encoder Interface Mode

9-21

120-035X-000D

Preliminary

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