Aaron Mears

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8 years, 1 month ago.

Creating a single pulse from clock when using TPM channels KL25Z

I'm working on something right now where I need a 10us pulse to trigger a device. I am using TPM0 and the internal clock which is at 41.94Mhz and the output set to a high pulse. I added a push button set up so when it is pushed there is output on another specified pin. I have had no problem creating a waveform that has a 10us period, but the problem I can't figure out is how I can isolate it and get just one of those pulses? Right now when the button is pushed I get the 100kHz square wave that is at 50% duty cycle, which I specified. Can someone tell me how I can get it to do just one pulse and stop?

1 Answer

Paul Staron
8 years, 1 month ago.

You could try this, very basic but should give you a 10uS pulse. Not sure which pins are interruptible on the KL25.

Best not to put a 'wait' in your interrupt callback.

snip

#include "mbed.h"
 
InterruptIn button(PTC1);  // switch to ground.
DigitalOut pulse(PTB0);
 
int IRQ; 
 
void IRQ_callback()
{
    IRQ=1;
}
 
int main() { 
    
    button.mode(PullUp);
    button.fall(IRQ_callback); 
  
    while(1) {
    
        if (IRQ==1) { // Button is pressed
        
            pulse=1;
        
            wait_us(10);
        
            pulse=0;
            
            while(!button){}   //add some debounce, wait till button released after pulse has fired
        
            IRQ=0;
        }
    }
}