Encoder Interface Mode; Figure 146. Clearing Timx Ocxref - ST STM32F205 series Reference Manual

General-purpose timers (TIM2 to TIM5)
1. The external trigger prescaler should be kept off: bits ETPS[1:0] in the TIMx_SMCR
register are cleared to 00.
2. The external clock mode 2 must be disabled: bit ECE in the TIM1_SMCR register is
cleared to 0.
3. The external trigger polarity (ETP) and the external trigger filter (ETF) can be
configured according to the application's needs.
Figure 146
for both values of the OCxCE enable bit. In this example, the timer TIMx is programmed in
PWM mode.
OCxREF (OCxCE = '0')
OCxREF (OCxCE = '1')
1. In case of a PWM with a 100% duty cycle (if CCRx>ARR), OCxREF is enabled again at the next counter
overflow.
14.3.12

Encoder interface mode

To select Encoder Interface mode write SMS='001 in the TIMx_SMCR register if the counter
is counting on TI2 edges only, SMS=010 if it is counting on TI1 edges only and SMS=011 if
it is counting on both TI1 and TI2 edges.
Select the TI1 and TI2 polarity by programming the CC1P and CC2P bits in the TIMx_CCER
register. CC1NP and CC2NP must be kept cleared. When needed, program the input filter
as well.
The two inputs TI1 and TI2 are used to interface to an incremental encoder. Refer to
Table 59. 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) assuming that it is enabled (CEN bit in
TIMx_CR1 register written to '1). 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, the DIR bit in the TIMx_CR1 register is modified by hardware
accordingly. The DIR bit is calculated at each transition on any input (TI1 or TI2), whatever
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 ARR or ARR down to 0 depending on the direction). So the user
402/1378
shows the behavior of the OCxREF signal when the ETRF input becomes high,

Figure 146. Clearing TIMx OCxREF

(CCRx)
Counter (CNT)
ETRF
RM0033 Rev 8
ETRF becomes high
ETRF still high
RM0033
MS37368V1