Pulse Capture

Purpose

Time-stamp edges of a pulse train

Library

STM32

Description

The capture blocks allows timestamping signal transitions (events) on input pins, e.g. for period and/or duty cycle measurements. The timestamps are made available on the block output c.

The output v is 1 for one simulation step after an event has been triggered, 0 otherwise. The output o is set to 1 if more than one capture event happened during the last model step. This indicates an overcapture state. It is not possible to deduce how many times the event was capture in the last model step. Overcapture events should therefore be avoided to ensure a reliable pulse detection. The output o is automatically cleared after it has been read.

The pulse capture block can be used in either PWM capture Mode or as Individual channels.

In PWM capture mode, one channel of the selected TIM unit can be used to get information about the period and duty cycle of the captured PWM signal. The first signal of the c output reflects the measured period, the second signal of the c output can be used to calculate the duty cycle.

When configured as Individual channels, up to three channels can be used to capture edges on individual signals. Also, the outputs c, v and o are vectorized signals if the block uses multiple channels.

The figure below illustrates with an example how the different output signals behave if Mode is set to Individual channels. The channels 1 and 2 are configured as described in the following table:

Channel	Edge	Prescale
1	Rising	every 2nd event
2	Falling	every 4th event

Fig. 28 An illustrative example for different capture settings when the Pulse Capture block is used with individual channels (channel 1 in red, channel 2 in blue).

If multiple capture events happen inside a model step the overcapture output will output a 1 at the end of the respective model step. The counter is operated in free-running mode and therefore not reset by a capture event. To calculate the period of the pulse input signal one has to calculate the difference between two consecutive capture events.

Parameters

Main

TIM unit

Selects the timer unit to use.

Mode

Specifies the desired capture mode. If set to Individual channels the channels of the selected TIM unit can be used to capture up to three individual signals. The PWM capture mode facilitates the measurement of frequency and duty cycle. In PWM capture mode exactly one Channel has to be enabled.

Clock prescale

Specifies the desired prescale value.

Channel 1/2/3

Capture

Provides an option to disable or enable an input channel.

Edge

The edge detection trigger can be set on Rising, Falling or Either.

Prescale

Specifies the desired prescale value for an individual channel.

Port

Selects the port name of the capture channel.

Pin

Defines the pin number of the capture channel.