
Advanced-control timer (TIM1)
RM0453
770/1454
RM0453 Rev 2
The OPM waveform is defined by writing the compare registers (taking into account the
clock frequency and the counter prescaler).
•
The t
DELAY
is defined by the value written in the TIMx_CCR1 register.
•
The t
PULSE
is defined by the difference between the auto-reload value and the compare
value (TIMx_ARR - TIMx_CCR1).
•
Let’s say one want to build a waveform with a transition from ‘0’ to ‘1’ when a compare
match occurs and a transition from ‘1’ to ‘0’ when the counter reaches the auto-reload
value. To do this PWM mode 2 must be enabled by writing OC1M=111 in the
TIMx_CCMR1 register. Optionally the preload registers can be enabled by writing
OC1PE=’1’ in the TIMx_CCMR1 register and ARPE in the TIMx_CR1 register. In this
case one has to write the compare value in the TIMx_CCR1 register, the auto-reload
value in the TIMx_ARR register, generate an update by setting the UG bit and wait for
external trigger event on TI2. CC1P is written to ‘0’ in this example.
In our example, the DIR and CMS bits in the TIMx_CR1 register should be low.
Since only 1 pulse (Single mode) is needed, a 1 must be written in the OPM bit in the
TIMx_CR1 register to stop the counter at the next update event (when the counter rolls over
from the auto-reload value back to 0). When OPM bit in the TIMx_CR1 register is set to '0',
so the Repetitive Mode is selected.
Particular case: OCx fast enable:
In One-pulse mode, the edge detection on TIx input set the CEN bit which enables the
counter. Then the comparison between the counter and the compare value makes the
output toggle. But several clock cycles are needed for these operations and it limits the
minimum delay t
DELAY
min we can get.
If one wants to output a waveform with the minimum delay, the OCxFE bit can be set in the
TIMx_CCMRx register. Then OCxRef (and OCx) are forced in response to the stimulus,
without taking in account the comparison. Its new level is the same as if a compare match
had occurred. OCxFE acts only if the channel is configured in PWM1 or PWM2 mode.
25.3.21 Retriggerable one pulse mode
This mode allows the counter to be started in response to a stimulus and to generate a
pulse with a programmable length, but with the following differences with Non-retriggerable
one pulse mode described in
–
The pulse starts as soon as the trigger occurs (no programmable delay)
–
The pulse is extended if a new trigger occurs before the previous one is completed
The timer must be in Slave mode, with the bits SMS[3:0] = ‘1000’ (Combined Reset + trigger
mode) in the TIMx_SMCR register, and the OCxM[3:0] bits set to ‘1000’ or ‘1001’ for
Retrigerrable OPM mode 1 or 2.
If the timer is configured in Up-counting mode, the corresponding CCRx must be set to 0
(the ARR register sets the pulse length). If the timer is configured in Down-counting mode,
CCRx must be above or equal to ARR.
Note:
The OCxM[3:0] and SMS[3:0] bit fields are split into two parts for compatibility reasons, the
most significant bit are not contiguous with the 3 least significant ones.
This mode must not be used with center-aligned PWM modes. It is mandatory to have
CMS[1:0] = 00 in TIMx_CR1.