lpc used as comparator

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by CroesJeroen on Mon Aug 27 04:03:54 MST 2012
Hello sir/madam.

I'm trying to use a input (gpio) as input for the comparator0 (+ input) and the - input of the comparator0 from the voltage divider ( set to Vdd/2). So the output of the comp go's high if I apply a voltage higher than vdd/2 and an interrupt is thrown.

The output of the comparator is always high even when no voltage is applied at the + input. The used microcontroller = LPC1227.

Here is the code :

#define PullUpDis  (1<<4) // default enabled
#define AnalogMode  (1<<7) // enable analog mode

#defineGPIO0_Clock  (1<<31)
#define Compare_CLK       (1<<20)// enable clock for comparator module
#define PowerCMP   ((1<<3)|(1<<15))// enable BOD en Comparator module in PDRUNCFG

#define CMP0_EN (1)// enable comparator module 0

#define CMPIEV (1<<3)// activate interrupt on rising edge
#define ACMP0_I0 (1<<8)// use ACMP0_O input

#define INTCOMPCLR (1<<20)// bit to reset the interrupt status
#defineCMP0STAT (1<<21)//interrupt status of the comparator 0
#defineCMP1STAT (1<<22)//interrupt status of the comparator 1

#defineVLADEN (1)// enable ladder module ( 32 levels, 0 to 3V3)
#define VSEL (10000<<1)

#define VLADVDDREF (1<<6)// use internal 3V3 voltage to take a level from


void InitCMP(void){

LPC_IOCON->PIO0_19|=0x2; // select as input for comparator(ACMP0_O)
LPC_IOCON->PIO0_19&=(~PullUpDis);//disable pullup
LPC_IOCON->PIO0_19&=(~AnalogMode);//enable analog mode
LPC_SYSCON->PDRUNCFG&=(~PowerCMP); // power the comparator module
LPC_ACOMP->VLAD|=(VLADEN|VSEL|VLADVDDREF); // enable voltage ladder, select reference 3.3V, set voltage to 1.66V
LPC_ACOMP->CMP|=(CMP0_EN|CMPIEV|ACMP0_I0|INTCOMPCLR); // enable comparator, use rising edge, positieve input opamp = input ACMP0_I0 , negative = voltage ladder


void COMP_IRQHandler(void){

uint8_t dummy=0;


Hopefully you guys can point me out why the output of comparator 0 is high even when no voltage is applied to the input and also when a voltage is applied, the interrupt doesnt hit..