PIC10F322 Applications – Basic Astable Using NCO (Numerically Controlled Oscillator)

PIC10F322 Applications – Basic Astable Using NCO (Numerically Controlled Oscillator)

The code (basic_astable_nco.c) and headers can be found in my GitHub here – https://github.com/JamieStarling/MCU_FUN/tree/master/Microchip/PIC10F322/

The last post I mentioned about the NCO – (Numerically Controlled Oscillator). In short without too much hair loss you can get a astable output on PORTA.2 up to 500Kz. This frequency is also selectable. 

Here is the output at 500Khz, 

So, how do we change it.. Well in the code below – there is a line..

setupNCO1(NCO_CLOCK_SOURCE_FOSC ,0xFFFF,NCO_FREQUNCY_MODE_FIXED);

The – 0XFFFF sets the Increment value of the adder.  With every pulse that comes into the NCO that value is added to the accumulator – which is 20bits in size. After two pulses the accumulator overflows – triggering the change on the output pin. 

So, how do we figure out other values – Here is the math  {Desired Freq}x 2 x 2^20 / {CPU Frequency}

Lets say, we want. 330Khz:

330,000 x 2 = 660,000 x 1048576 = 692,060,160,000 / 16000000 = 43,253.76 – Round it to 43,254 or (0xA8F6)

We replace – 0xFFFF with 0xA8F6 – to get… very very close to 330Khz.  There is some jitter but that is expected. 

Anyway – the code is below – or you can find it all in my Github page. 

/*
 * File:   astable_nco.c
 * Author: Jamie
 *
 * Created on August 15, 2020, 10:39 AM
 */


#include "includes/10F322_deviceconfig.h"
#include "includes/nco.h"
#include "includes/gpio.h"
#include "includes/osc.h"

void main(void)
{
    cpuFreqSelect(MHZ16);
    pinMode(2,OUTPUT);    
    setupNCO1(NCO_CLOCK_SOURCE_FOSC ,0xFFFF,NCO_FREQUNCY_MODE_FIXED); //500Khz Output
    
    

    while(1){}
   
}