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S32K144_Edge Capure using GPIO or FTM

Question asked by KWAK D.Y on Jun 11, 2018
Latest reply on Jun 15, 2018 by KWAK D.Y

▶ Goal:  To calculate the pulse interval.(Using EVBs)

▶ Description

 (1) GPIO pin is set to interrupt when falling or rising edge.(Pin No: EVB1_A)

 (2) And a pulse of 250us cycle is output to the other pin.(Pin No: EVB1_B)

 (3) Set the FTM timer.

 (4) EVB1_A and  EVB1_B are connected.

 (5) When the falling and rising edge of the pulse occurs, the interrupt is executed well and it measures the reading of the time counter when the interrupt occurs. (6)The result is a success of 250us.


▶ problem

  The problem is when two EVBs are used.

  (1) EVB1 and EVB2 Download the same code as above.

  (2) Connect the EVB2 pulse output signal to the EVB1 Capture input pin. Then connect the ground pins to each other.

  (3) And if you calculate the cycle, 30 ~ 40 us is measured instead of 250us.

  (4) When measured with an oscilloscope, a pulse of 250us is output.


▶ Question

  I wonder why 30 ~ 40 us is measured when receiving 250us pulse signal from other board.

  The same phenomenon occurs when using FTM Capture instead of GPIO.