Pwm Input Mode; Forced Output Mode; Figure 101. Pwm Input Mode Timing - ST STM32F101 Series Reference Manual

RM0008
13.4.6

PWM input mode

This mode is a particular case of input capture mode. The procedure is the same except:
Two ICx signals are mapped on the same TIx input.
These 2 ICx signals are active on edges with opposite polarity.
One of the two TIxFP signals is selected as trigger input and the slave mode controller
is configured in reset mode.
For example, you can measure the period (in TIMx_CCR1 register) and the duty cycle (in
TIMx_CCR2 register) of the PWM applied on TI1 using the following procedure (depending
on CK_INT frequency and prescaler value):
Select the active input for TIMx_CCR1: write the CC1S bits to 01 in the TIMx_CCMR1
register (TI1 selected).
Select the active polarity for TI1FP1 (used both for capture in TIMx_CCR1 and counter
clear): write the CC1P bit to '0' (active on rising edge).
Select the active input for TIMx_CCR2: write the CC2S bits to 10 in the TIMx_CCMR1
register (TI1 selected).
Select the active polarity for TI1FP2 (used for capture in TIMx_CCR2): write the CC2P
bit to '1' (active on falling edge).
Select the valid trigger input: write the TS bits to 101 in the TIMx_SMCR register
(TI1FP1 selected).
Configure the slave mode controller in reset mode: write the SMS bits to 100 in the
TIMx_SMCR register.
Enable the captures: write the CC1E and CC2E bits to '1' in the TIMx_CCER register.

Figure 101. PWM input mode timing.

TIMx_CCR1
13.4.7

Forced output mode

In output mode (CCxS bits = 00 in the TIMx_CCMRx register), each output compare signal
(OCxREF and then OCx) can be forced to active or inactive level directly by software,
independently of any comparison between the output compare register and the counter.
To force an output compare signal (ocxref/OCx) to its active level, you just need to write 101
in the OCxM bits in the corresponding TIMx_CCMRx register. Thus ocxref is forced high
(OCxREF is always active high) and OCx get opposite value to CCxP polarity bit.
TI1
0004 0000
TIMx_CNT
TIMx_CCR2
IC1 Capture
period measurement
reset counter
General purpose timer (TIMx)
0001 0002 0003
0004
0002
IC2 Capture
pulse width measurement
0004 0000
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