STM32W108HB datasheet(178/278 Pages) STMICROELECTRONICS

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General-purpose timers

STM32W108HB STM32W108CC STM32W108CB STM32W108CZ

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Doc ID 16252 Rev 14

A special case: OCy fast enable

In one-pulse mode, the edge detection on the TIy input sets the CEN bit, which enables the

counter. Then the comparison between the counter and the compare value toggles the

output. However, several clock cycles are needed for this operation, and it limits the

minimum delay (tDELAY min) achievable.

To output a waveform with the minimum delay, set the OCyFE bit in the TIMx_CCMR1

comparison into account. Its new level is the same as if a compare match had occurred.

OCyFE acts only if the channel is configured in PWM mode 1 or 2.

10.1.11

Encoder interface mode

To select encoder interface mode, write SMS = 001 in the TIMx_SMCR register to count

only TI2 edges, SMS = 010 to count only TI1 edges, and SMS = 011 to count both TI1 and

TI2 edges.

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

The two inputs TI1 and TI2 are used to interface to an incremental encoder (see Table 34).

Assuming that it is enabled, (the CEN bit in the TIMx_CR1 register written to 1) the counter

is clocked by each valid transition on TI1FP1 or TI2FP2 (TI1 and TI2 after input filter and

polarity selection, TI1FP1 = TI1 if not filtered and not inverted, TI2FP2 = TI2 if not filtered

and not inverted.) The sequence of transitions of the two inputs is evaluated, and generates

count pulses as well as the direction signal. Depending on the sequence, the counter counts

up or down, and hardware modifies the DIR bit in the TIMx_CR1 register accordingly. The

DIR bit is calculated at each transition on any input (TI1 or TI2), whether the counter is

counting on TI1 only, TI2 only, or both TI1 and TI2.

Encoder interface mode acts simply as an external clock with direction selection. This

means that the counter just counts continuously between 0 and the auto-reload value in the

TIMx_ARR register (0 to TIMx_ARR or TIMx_ARR down to 0 depending on the direction),

so TIMx_ARR must be configured before starting. In the same way, the capture, compare,

prescaler, and trigger output features continue to work as normal.

In this mode the counter is modified automatically following the speed and the direction of

the incremental encoder, and therefore its contents always represent the encoder's position.

The count direction corresponds to the rotation direction of the connected sensor. Table 34

summarizes the possible combinations, assuming TI1 and TI2 do not switch at the same

time.

STM32W108HB Datasheet(PDF) 178 Page - STMicroelectronics