STM8S datasheet(185/467 Pages) STMICROELECTRONICS

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RM0016

16-bit advanced control timer (TIM1)

261

17.5.10

Encoder interface mode

Encoder interface mode is typically used for motor control. It can be selected by writing:

•

SMS = 001 in the TIM1_SMCR register if the counter is counting on TI2 edges only

•

SMS = 010 if the counter is counting on TI1 edges only

•

SMS = 011 if the counter is counting on both TI1 and TI2 edges

Select the TI1 and TI2 polarity by programming the CC1P and CC2P bits in the

TIM1_CCER1 register. When needed, the input filter can also be programmed.

The two inputs TI1 and TI2 are used to interface an incremental encoder (see Table 37). If

the counter is enabled (when the CEN bit in the TIM1_CR1 register is written to 1), it is

clocked by each valid transition on TI1FP1 or TI2FP2 (see Figure 64: Input stage of TIM 1

channel 1). The transition sequences of the two inputs (TI1 and TI2) are evaluated and

generate count pulses and a direction signal. Depending on the sequence, the counter

counts up or down, and the DIR bit in the TIM1_CR1 register is modified accordingly by

hardware. The DIR bit is calculated at each transition based on inputs from either TI1 or TI2.

without this being dependent on whether the counter is counting pulses on TI1, TI2 or both.

Encoder interface mode acts as an external clock with direction selection. The counter

counts continuously between 0 and the auto-reload value in the TIM1_ARR register (0 to

ARR or ARR down to 0 depending on the direction). TIM1_ARR must be configured before

starting. The capture, compare, prescaler, and trigger output features continue to work as

normal in this mode. Encoder mode and external clock mode 2 are not compatible and must

not be selected together.

In encoder interface mode, the counter is modified automatically depending on the speed

and the direction of the incremental encoder. The content of the counter therefore always

represents the encoder's position. The count direction corresponds to the rotation direction

of the connected sensor. Table 37 summarizes the possible combinations of counting

directions and encoder signals, assuming that TI1 and TI2 do not switch at the same time.

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

interface logic. However, comparators are normally used to convert the encoder’s

differential outputs to digital signals. This greatly increases noise immunity. The third

encoder output which indicates the mechanical zero position, may be connected to an

external interrupt input and trigger a counter reset.

Table 37. Counting direction versus encoder signals

Active edge

Level on opposite

signal

(TI1FP1 for TI2,

TI2FP2 for TI1)

TI1FP1 signal

TI2FP2 signal

Rising

Falling

Rising

Falling

Counting on

TI1 only

High

Down

No count

Low

Down

No count

Counting on

TI2 only

High

No count

Down

Low

No count

Down

Counting on

both TI1 and

TI2

High

Down

Low

Down

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