EM357-RTR datasheet(120/241 Pages) SILABS

120 / 241 page

Rev 1.3

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Figure 9.7. Counter Timing Diagram, Internal Clock Divided by 1

Figure 9.8. Counter Timing Diagram, Internal Clock Divided by 4

9.3.2.3. Center-Aligned Mode (Up/Down Counting)

In center-aligned mode, the counter counts from 0 to the auto-reload value (contents of the TIMx_ARR register) – 1

and generates a counter overflow event, then counts from the autoreload value down to 1 and generates a counter

underflow event. Then it restarts counting from 0.

In this mode, the direction bit (TIM_DIR in the TIMx_CR1 register) cannot be written. It is updated by hardware and

gives the current direction of the counter.

The UEV can be generated at each counter overflow and at each counter underflow. Setting the TIM_UG bit in the

TIMx_EGR register by software or by using the slave mode controller also generates a UEV. In this case, the both

the counter and the prescaler’s counter restart counting from 0.

Software can disable the UEV by setting the TIM_UDIS bit in the TIMx_CR1 register. This avoids updating the

shadow registers while writing new values in the buffer registers. Then no UEV occurs until the TIM_UDIS bit has

been written to 0. However, the counter continues counting up and down, based on the current auto-reload value.

In addition, if the TIM_URS bit in the TIMx_CR1 register is set, setting the TIM_UG bit generates a UEV, but

without setting the INT_TIMUIF flag. Thus no interrupt request is sent. This avoids generating both update and

capture interrupt when clearing the counter on the capture event.

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