ST STM32L0x3 User Manual

RM0367 Rev 7 567/1043
RM0367 General-purpose timers (TIM21/22)
601
Figure 178. Output stage of capture/compare channel (channel 1 and 2)
The capture/compare block is made of one preload register and one shadow register. Write
and read always access the preload register.
In capture mode, captures are actually done in the shadow register, which is copied into the
preload register.
In compare mode, the content of the preload register is copied into the shadow register
which is compared to the counter.
22.3.5 Input capture mode
In Input capture mode, the Capture/Compare Registers (TIMx_CCRx) are used to latch the
value of the counter after a transition detected by the corresponding ICx signal. When a
capture occurs, the corresponding CCXIF flag (TIMx_SR register) is set and an interrupt or
a DMA request can be sent if they are enabled. If a capture occurs while the CCxIF flag was
already high, then the over-capture flag CCxOF (TIMx_SR register) is set. CCxIF can be
cleared by software by writing it to ‘0’ or by reading the captured data stored in the
TIMx_CCRx register. CCxOF is cleared when it is written with 0.
The following example shows how to capture the counter value in TIMx_CCR1 when TI1
input rises. To do this, use the following procedure:
1. Select the active input: TIMx_CCR1 must be linked to the TI1 input, so write the CC1S
bits to ‘01’ in the TIMx_CCMR1 register. As soon as CC1S becomes different from ‘00’,
the channel is configured in input mode and the TIMx_CCR1 register becomes read-
only.
2. Program the appropriate input filter duration in relation with the signal connected to the
timer (when the input is one of the TIx (ICxF bits in the TIMx_CCMRx register). Let’s
imagine that, when toggling, the input signal is not stable during at must 5 internal clock
cycles. We must program a filter duration longer than these 5 clock cycles. We can
validate a transition on TI1 when 8 consecutive samples with the new level have been
MSv33714V1
TIMx_CCER
Output
mode
controller
CNT > CCR2
CNT = CCR2
TIMx_CCMR1
0
1
TIMx_CCER
Output
enable
circuit
OCx
CCxE
To the master
mode controller
OCx_REF
OCxM[2:0]
CCxP
ETRF

ST STM32L0x3 Specifications

General

Brand	ST
Model	STM32L0x3
Category	Microcontrollers
Language	English