EM351_12 Datasheet, PDF (145/245 Pages) Silicon Laboratories – High-Performance, Integrated ZigBee/802.15.4 System-on-Chip

EM351 / EM357
Figure 9-26 gives an example of counter behavior when IC1FP1 polarity is inverted (same configuration as
above except TIM_CC1P = 1).
Figure 9-26. Example of Encoder Interface Mode with IC1FP1 Polarity Inverted
The timer configured in encoder interface mode provides information on a sensor’s current position. To obtain
dynamic information (speed, acceleration/deceleration), measure the period between two encoder events
using a second timer configured in capture mode. The output of the encoder that indicates the mechanical
zero can be used for this purpose. Depending on the time between two events, the counter can also be read
at regular times. Do this by latching the counter value into a third input capture register. (In this case the
capture signal must be periodic and can be generated by another timer).
9.3.12 Timer Input XOR Function
The TIM_TI1S bit in the TIM1_CR2 register allows the input filter of channel 1 to be connected to the output of
a XOR gate that combines the three input pins TIMxC2 to TIMxC4.
The XOR output can be used with all the timer input functions such as trigger or input capture. It is especially
useful to interface to Hall effect sensors.
9.3.13 Timers and External Trigger Synchronization
The timers can be synchronized with an external trigger in several modes: reset mode, gated mode, and
trigger mode.
9.3.13.1 Slave Mode: Reset Mode
Reset mode reinitializes the counter and its prescaler in response to an event on a trigger input. Moreover, if
the TIM_URS bit in the TIMx_CR1 register is low, a UEV is generated. Then all the buffered registers
(TIMx_ARR, TIMx_CCRy) are updated.
In the following example, the up-counter is cleared in response to a rising edge on the TI1 input:
 ^{Configure the channel 1 to detect rising edges on TI1:}
• ^{Configure the input filter duration. In this example, no filter is required so TIM_IC1F = 0000.}
• ^{The capture prescaler is not used for triggering, so it is not configured.}
• ^{The TIM_CC1S bits select the input capture source only, TIM_CC1S = 01 in the TIMx_CCMR1 register.}
• ^{Write TIM_CC1P = 0 in the TIMx_CCER register to validate the polarity, and detect rising edges}
only.
 ^{Configure the timer in reset mode: Write TIM_SMS = 100 in the TIMx_SMCR register.}
 ^{Select TI1 as the input source by writing TIM_TS = 101 in the TIMx_SMCR register.}
 ^{Start the counter: Write TIM_CEN = 1 in the TIMx_CR1 register.}
9-22
Final
120-035X-000M