Timer Input Xor Function; Interfacing With Hall Sensors - ST STM32F100 Series Reference Manual

RM0041
12.3.17

Timer input XOR function

The TI1S bit in the TIMx_CR2 register, allows the input filter of channel 1 to be connected to
the output of a XOR gate, combining the three input pins TIMx_CH1, TIMx_CH2 and
TIMx_CH3.
The XOR output can be used with all the timer input functions such as trigger or input
capture. An example of this feature used to interface Hall sensors is given in
Section 12.3.18.
12.3.18

Interfacing with Hall sensors

This is done using the advanced-control timers (TIM1) to generate PWM signals to drive the
motor and another timer TIMx (TIM2, TIM3, TIM4 or TIM5) referred to as "interfacing timer"
in Figure
and TIMx_CH3) connected through a XOR to the TI1 input channel (selected by setting the
TI1S bit in the TIMx_CR2 register).
The slave mode controller is configured in reset mode; the slave input is TI1F_ED. Thus,
each time one of the 3 inputs toggles, the counter restarts counting from 0. This creates a
time base triggered by any change on the Hall inputs.
On the "interfacing timer", capture/compare channel 1 is configured in capture mode,
capture signal is TRC (see
elapsed between 2 changes on the inputs, gives information about motor speed.
The "interfacing timer" can be used in output mode to generate a pulse which changes the
configuration of the channels of the advanced-control timer (TIM1) (by triggering a COM
event). The TIM1 timer is used to generate PWM signals to drive the motor. To do this, the
interfacing timer channel must be programmed so that a positive pulse is generated after a
programmed delay (in output compare or PWM mode). This pulse is sent to the advanced-
control timer (TIM1) through the TRGO output.
Example: the user wants to change the PWM configuration of the advanced-control timer
TIM1 after a programmed delay each time a change occurs on the Hall inputs connected to
one of the TIMx timers.
•
Configure 3 timer inputs ORed to the TI1 input channel by writing the TI1S bit in the
TIMx_CR2 register to '1',
•
Program the time base: write the TIMx_ARR to the max value (the counter must be
cleared by the TI1 change. Set the prescaler to get a maximum counter period longer
than the time between 2 changes on the sensors,
• Program channel 1 in capture mode (TRC selected): write the CC1S bits in the
TIMx_CCMR1 register to '11'. The user can also program the digital filter if needed,
•
Program channel 2 in PWM 2 mode with the desired delay: write the OC2M bits to '111'
and the CC2S bits to '00' in the TIMx_CCMR1 register,
•
Select OC2REF as trigger output on TRGO: write the MMS bits in the TIMx_CR2
register to '101',
In the advanced-control timer TIM1, the right ITR input must be selected as trigger input, the
timer is programmed to generate PWM signals, the capture/compare control signals are
preloaded (CCPC=1 in the TIMx_CR2 register) and the COM event is controlled by the
trigger input (CCUS=1 in the TIMx_CR2 register). The PWM control bits (CCxE, OCxM) are
written after a COM event for the next step (this can be done in an interrupt subroutine
generated by the rising edge of OC2REF).
83. The "interfacing timer" captures the 3 timer input pins (TIMx_CH1, TIMx_CH2,
Figure 66). The captured value, which corresponds to the time
RM0041 Rev 6
Advanced-control timer (TIM1)
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