RM0312 datasheet(128/275 Pages) STMICROELECTRONICS

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16-bit general purpose timer (TIM2/TIM3)

RM0312

128/275

DocID022352 Rev 3

17.5

TIMx capture/compare channels

The timer I/O pins (TIMx_CHi) can be configured either for input capture or output compare

functions. The choice made by configuring the CCiS channel selection bits in the

capture/compare channel mode register (TIMx_CCMRi), where i is the channel number.

Each Capture/Compare channel is built around a capture/compare register (including a

shadow register), an input stage for capture (with digital filter, multiplexing and prescaler)

and an output stage (with comparator and output control).

Figure 48. Capture/compare channel 1 main circuit

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.

When the channel is configured in output mode (CCiS=0b00 in the TIMx_CCMRi register)

where i is the channel number, the TIMx_CCRi register can be accessed without any

restriction.

When the channel is configured in input mode, the sequence for reading the TIMx_CCRi

of the counter is captured into the TIMx_CCRi shadow register. Then this value is loaded

into the preload register, except during the read sequence, when the preload register is

frozen.

CC1E

Capture/Compare shadow Register

comparator

Capture/Compare Preload Register

Counter

ic1ps

CC1S[0]

CC1S[1]

capture

input

mode

read CCR1H

read CCR1L

read_in_progress

capture_transfer

CC1S[0]

CC1S[1]

write CCR1H

write CCR1L

write_in_progress

output

mode

UEV

OC1PE

(from time

compare_transfer

TIMx_CCMR1

OC1PE

base unit)

CNT>CCR1

CNT=CCR1

TIMx_EGR

CC1G

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