Microcontrollers excel at one thing and that thing is computing on a power budget. Microcontrollers are many times battery operated devices and for that reason it is sometimes necessary to have mechanisms to reduce power consumption. While reducing the clock speed or the CPU and peripherals is one way to reduce power consumption the PIC32 includes two power saving modes which are the IDLE mode and the SLEEP mode to reduce power consumption. In this post we use the PIC32MX270F256D in IDLE and SLEEP modes.

PIC32 Idle and Sleep

The PIC32MX270F256D includes two categories of power saving modes. These are the idle and sleep methods  of reducing power consumption.

In idle mode, the CPU stops but SYSCLK still operates which allows the periherals to continue to operate. The SIDL bit can be set to allow certain peripherals to operate in IDLE mode.

In sleep mode the microcontroller has maximum power consumption savings and SYSCLK as well as the CPU clock is stopped.

The “wait” instruction is given via assembly to allow the microcontroller to enter into a power saving mode. Though some peripherals can wake a device from sleep mode, in our example we will not be using any peripheral to wake from sleep.


Only the CP2104 USB-UART bridge is connected to the microcontroller.

C Program

 * File: Main.c
 * Author: Armstrong Subero
 * Processor: PIC32MX270F256D w/Ext OSC @ 4MHz, PLL to 48 MHz, 3.3v
 * Program: 13_Idle_Sleep
 * Compiler: XC32 (v1.44, MPLAX X v4.00)
 * Program Version: 1.0
 * Program Description: This Program Allows PIC32MX270F256D to demonstrate the
 *                      IDLE and SLEEP modes of the microcontroller.
 * Hardware Description: An CP2104 USB-UART converter is connected to PINC5
 * Change History:
 * Author             Rev     Date          Description
 * Armstrong Subero   1.0     03/04/2018    Initial Release.
 * Created April 3nd, 2018, 9:40 PM

 Includes and defines
#include <xc.h>
#include <stdio.h>
#include <stdlib.h>
#include "PIC32MX270_STD.h"
#include "Delay.h"
#include "uart1.h"

#define LED LATBbits.LATB14

* Function Name: void initMain (void)
* Specification: initializes main
void initMain(void)
    uc_init();              // initialize microcontroller
    TRISBbits.TRISB14 = 0;  // set PINB1 as output
    // unlock PPS
    CFGCONbits.IOLOCK = 0;

    RPC5Rbits.RPC5R = 0x0001;   //RC5->UART1 TX

    // lock PPS
    CFGCONbits.IOLOCK = 1; 

* Function Name: void main (void)
* Specification: main function
void main(void) {
    initMain();         // initializes main function
    #define SLEEP_DEMO
      // configure printf to use UART1
      __XC_UART = 1;
#ifdef IDLE_DEMO
      printf("Going to IDLE\n");
      delay_ms(5000);       // delay 5 seconds
      SYSKEY = 0x0;         // Write invalid key to force lock
      SYSKEY = 0xAA996655;  // Write Key1 to SYSKEY
      SYSKEY = 0x556699AA;  // Write Key2 to SYSKEY
      OSCCONCLR = 0x10;     // Set the power-saving mode to an idle mode
      SYSKEY = 0x0;         // Write invalid key to force lock
      asm volatile ( "wait" ); // Put device in selected power-saving mode
      printf("After Idle dose not run!\n");
#elif defined SLEEP_DEMO
      OSCCONSET = 0x10;           // set Power-Saving mode to Sleep
      printf ("Going to SLEEP\n");
      asm volatile("wait");       // put device in sleep mode
      printf("After sleep dose not run");

The microcontroller can be put into either idle mode or sleep demo mode by changing the define statement in main. The microcontroller measured a power consumption of 14.4 mA power consumption in sleep and idle mode, and a normal operating current of 29.4 mA.

Link to Project

You can download the entire project here!

Sleep and Idle Project



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