General-purpose timers (TIM2/TIM3/TIM4/TIM5) RM0440
1274/2126 RM0440 Rev 4
Figure 404. Extended pulse width in case of concurrent triggers
29.4.18 Encoder interface mode
Quadrature encoder
To select Encoder Interface mode write SMS=‘0001 in the TIMx_SMCR register if the
counter is counting on tim_ti1 edges only, SMS=0010 if it is counting on tim_ti2 edges only
and SMS=0011 if it is counting on both tim_ti1 and tim_ti2 edges.
Select the tim_ti1 and tim_ti2 polarity by programming the CC1P and CC2P bits in the
TIMx_CCER register. CC1NP and CC2NP must be kept cleared. When needed, the input
filter can be programmed as well.
The two inputs tim_ti1 and tim_ti2 are used to interface to an incremental encoder. Refer to
Table 279. The counter is clocked by each valid transition on tim_ti1fp1 or tim_ti2fp2 (tim_ti1
and tim_ti2 after input filter and polarity selection, tim_ti1fp1=tim_ti1 if not filtered and not
inverted, tim_ti2fp2=tim_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 (tim_ti1 or
tim_ti2), whatever the counter is counting on tim_ti1 only, tim_ti2 only or both tim_ti1 and
tim_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
TIMx_ARR must be configured before starting. In the same way, the capture, compare,
prescaler, trigger output features continue to work as normal. Encoder mode and External
clock mode 2 are not compatible and must not be selected together.
In this mode, the counter is modified automatically following the speed and the direction of
the
quadrature encoder and its content, therefore, always represents the encoder’s position.
The count direction correspond to the rotation direction of the connected sensor. The table
summarizes the possible combinations, assuming tim_ti1 and tim_ti2 do not switch at the
same time.
MSv62348V1
Trigger CMP3
tim_oc3
Trigger CMP4
tim_oc4
Extended pulsewidth
due to overlapping
CMP4 trigger
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