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   = 0x16;  // Enable rising edge interrupt and flag (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 names' column in above table 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.
• A special case is the NC pinname. Declaring this pin will connect the internal 6-bit DAC0.
  

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 myled(LED1); // Blue LED (blinks at a constant rate)
DigitalOut cmpled(LED2); // Green LED (lit when comparator threshold is reached)
DigitalOut cmp_en (PTD5); // Op-amp enable pin on Wi-Go board
ComparatorIn compi(PTC8, NC); // light sensor comparator input

// Comparator callback function
void cmp_ISR(unsigned int cmp_ret)
{
    if ((cmp_ret & CMP_SCR_CFR_MASK)==CMP_SCR_CFR_MASK)
    {
        printf("<INT=Rising edge on HSCMP0>\n");
    }
    if ((cmp_ret & CMP_SCR_CFF_MASK)==CMP_SCR_CFF_MASK)
    {
        printf("<INT=Falling edge on HSCMP0>\n ");
    }
}

int main()
{
    cmp_en = 1;

    compi._callbackISR(&cmp_ISR);               // Set comparator interrupt callback to cmp_ISR
    compi.treshold(0x20);                       // Set comparator threshold to 1.65V = 32 * 3.3V / 64

    while(1)
    {
        myled = 1;
        wait(1);
        myled = 0;
        wait(0.2);
        if (compi.status() == 0x01)         // Poll comparator output
        {
            cmpled = 0;
        }
        else
        {
            cmpled = 1;
        }
    }
}

Notes

• When interrupts are enabled, we need to declare a user callback function AND initialise the pointer to this function
  example:

compi._callbackISR(&cmp_ISR);

• Use of an unsigned int in the user declared callback function is mandatory.
• The interrupt returns two possible values:
  • CMP_SCR_CFR_MASK to indicate a rising interrupt (when enabled).
  • CMP_SCR_CFF_MASK to indicate a falling interrupt (when enabled).
• 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).
  • Connecting the comparator output to a physical pin.
  • DMA transfer.