Advanced-control timer (TIM1) RM0444
568/1390 RM0444 Rev 5
21.3.18 Clearing the OCxREF signal on an external event
When ETRF is chosen, ETR must be configured as follows:
1. The External Trigger Prescaler should be kept off: bits ETPS[1:0] of the TIMx_SMCR
register set to ‘00’.
2. The external clock mode 2 must be disabled: bit ECE of the TIMx_SMCR register set to
‘0’.
3. The External Trigger Polarity (ETP) and the External Trigger Filter (ETF) can be
configured according to the user needs.
Figure 149 shows the behavior of the OCxREF signal when the ETRF Input becomes High,
for both values of the enable bit OCxCE. In this example, the timer TIMx is programmed in
PWM mode.
Figure 149. Clearing TIMx OCxREF
Note: In case of a PWM with a 100% duty cycle (if CCRx>ARR), then OCxREF is enabled again at
the next counter overflow.
The OCxREF signal of a given channel can be cleared when a high level is applied on the
ocref_clr_int input (OCxCE enable bit in the corresponding TIMx_CCMRx register set to 1).
OCxREF remains low until the next update event (UEV) occurs. This function can only be
used in Output compare and PWM modes. It does not work in Forced mode. ocref_clr_int
input can be selected between the OCREF_CLR input and ETRF (ETR after the filter) by
configuring the OCCS bit in the TIMx_SMCR register.
MS33105V2
(CCRx)
Counter (CNT)
ETRF
OCxREF
(OCxCE = ‘0’)
OCxREF
(OCxCE = ‘1’)
ocref_clr_int
becomes high
ocref_clr_int
still high
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