ST STM32F412 Reference Manual page 574

General-purpose timers (TIM9 to TIM14)
Bit 3 OC1PE: Output compare 1 preload enable
Note: The PWM mode can be used without validating the preload register only in one-pulse
Bit 2 OC1FE: Output compare 1 fast enable
Bits 1:0 CC1S: Capture/Compare 1 selection
Note: The CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).
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0: Preload register on TIMx_CCR1 disabled. TIMx_CCR1 can be written at anytime, the
new value is taken into account immediately
1: Preload register on TIMx_CCR1 enabled. Read/Write operations access the preload
register. TIMx_CCR1 preload value is loaded into the active register at each update event
mode (OPM bit set in the TIMx_CR1 register). Else the behavior is not guaranteed.
This bit is used to accelerate the effect of an event on the trigger in input on the CC output.
0: CC1 behaves normally depending on the counter and CCR1 values even when the
trigger is ON. The minimum delay to activate the CC1 output when an edge occurs on the
trigger input is 5 clock cycles
1: An active edge on the trigger input acts like a compare match on the CC1 output. Then,
OC is set to the compare level independently of the result of the comparison. Delay to
sample the trigger input and to activate CC1 output is reduced to 3 clock cycles. OC1FE
acts only if the channel is configured in PWM1 or PWM2 mode.
This bitfield defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10: CC1 channel is configured as input, IC1 is mapped on TI2
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode works only if an
internal trigger input is selected through the TS bit (TIMx_SMCR register)
RM0402 Rev 6
RM0402