KL25Z Comparator library¶

Comparator features¶

• Operational over the entire supply range
  
• Inputs may range from rail to rail
  
• Programmable hysteresis control
  
• Selectable interrupt on rising-edge, falling-edge, or both rising or falling edges of the comparator output
  
• Selectable inversion on comparator output
  
• Capability to produce a wide range of outputs such as:
  • Sampled
    
  • Windowed, which is ideal for certain PWM zero-crossing-detection applications
    
  • Digitally filtered:
    
    • Filter can be bypassed
      
    • Can be clocked via external SAMPLE signal or scaled bus clock
      
• External hysteresis can be used at the same time that the output filter is used for internal functions
  
• Two software selectable performance levels:
  • Shorter propagation delay at the expense of higher power
    
  • Low power, with longer propagation delay
    
• DMA transfer support ^{not yet implemented in this library}
  
  • A comparison event can be selected to trigger a DMA transfer
    
• Functional in all modes of operation
  
• The window and filter functions are not available in the following modes:
  • Stop
  • VLPS
  • LLS
  • VLLSx

Block diagram¶

Introduction¶

This library allows us to create comparator objects between different inputs.
The comparator + and - inputs can be routed to one out of eight reference inputs (see table).
Input selection

* Not yet implemented

Using the library¶

Selecting pins on initialisation
Upon initialisation, the comparator registers are set to following values:

    CMP0->CR0   = 0x00;  // Filter and digital hysteresis disabled
    CMP0->CR1   = 0x17;  // Continuous mode, high-speed compare, unfiltered output, output pin disabled
    CMP0->FPR   = 0x00;  // Filter disabled
    CMP0->SCR   = 0x06;  // Disable all interrupts and clear flags (flags are cleared by this write)
    CMP0->DACCR = 0xE0;  // DAC enabled, Vdd is 6bit reference, threshold set to 1/2 of full-scale (1.65V)

The library accepts two input parameters:
example:

ComparatorIn compi(PTC8, NC);

• First parameter : + input pin.
  
• Second parameter : - input pin.
  Every pin from the 'Pin name' column in (table 1) can be selected.
  

notes

• IN6 (internal 1V bandgap reference) has no pin name and is not selectable on init.
  However, we can use the switch_plus and switch_min functions to change the corresponding input to IN6.
• There are two special cases for the input parameters:
  • NC : Connect the internal 6-bit DAC0 to IN7.
  • PTE30 : configures PTE30 as 12-bit DAC0 output and connect to IN4.
    

Example
Following code demonstrates interrupt callback and polling mode.

/***********************************************************
CODE EXAMPLE FOR AMBIENT LIGHT SENSOR ON KL25Z + Wi-Go BOARD
 ***********************************************************/
#include "ComparatorIn.h"
#include "mbed.h"

DigitalOut blinker(LED_BLUE);
DigitalOut cmpled(LED_GREEN);
DigitalOut cmp_en (PTD5);
AnalogIn cmp_lvl (PTB0);
ComparatorIn compi(PTC8, NC); // in+ = PTC8, in- = internal 6-bit DAC 

// Comparator callback functions
void cmp_rise_ISR(void)
{
    cmpled = 0;
}

void cmp_fall_ISR(void)
{
    cmpled = 1;
}

int main()
{
    cmp_en = 1;
    cmpled = 1;

    compi.rising(&cmp_rise_ISR);                // Set pointer to rising interrupt function
    compi.falling(&cmp_fall_ISR);               // Set pointer to falling interrupt function
    compi.treshold(0.5);                        // Set comparator threshold to 1.65V = 32 * 3.3V / 64
    compi.int_en(1);                            // Enable comparator interrupts

    while(1)
    {
        printf("Light sensor : %7.5f Volt\n",cmp_lvl*3.3);
        blinker = 1;
        wait(1);
        blinker = 0;
        wait(0.2);
        if (compi.status() == 0x01)
        {
            printf("*** Treshold reached : %7.5f\n",cmp_lvl*3.3);
        }
    }
}

Notes

• When we enable the comparator interrupt, we need to declare user callback function(s) (rising and/or falling interrupt) AND initialise the function pointer(s).
  example:

compi.rising(&cmp_rise_ISR);
compi.falling(&cmp_fall_ISR);

• Currently, following functions are not yet implemented:
  • On the fly MUX switching for + input (switch_plus function).
  • On the fly MUX switching for - input (switch_min function).
  • DMA transfer.