STR720 datasheet(324/401 Pages) STMICROELECTRONICS

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STR720 - EXTENDED FUNCTION TIMER (EFT)

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21.3.8

Pulse Width Modulation Input

The PWM Input functionality enables the measurement of the period and the pulse width of an

external waveform. The initial edge is programmable.

It uses the two Input Capture registers and the Input signal of the Input Capture A module.

21.3.8.1 Procedure

The CR2 register must be programmed as needed for Interrupts and DMAs. To use pulse

width modulation mode select the following in the CR1 register:

– set the PWMI bit

– Select the first edge in IEDGA

– Select the second edge IEDGB as the negated of IEDGA

– Program the clock source and prescaler as needed

– Enable the counter setting the EN bit.

To have a coherent measure the interrupt/DMA should be linked to the Input Capture A

Interrupt, reading in ICAR the period value and in ICBR the pulse width.

To obtain the time values:

Where:

fAPB

= APB clock frequency

tPRESC

= Timer clock prescaler: (CC7..CC0)+1

The Input Capture A event causes the counter to be initialized to 0000h, allowing a new

measure to start. The first Input Capture on ICAPA do not generate the corresponding

interrupt request.

Period =

ICAR * fAPB

tPRESC

Pulse =

ICBR * fAPB

tPRESC

STR720 数据表(PDF) 324 Page - STMicroelectronics