pic16f877a multiple ADC problems..

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I have to sense two analogue voltages with the help of PIC16F877A

But the problem is that my Second Channel of ADC is not working....
Its value is not changing and remains same as that for the first conversion..

Here is my code

	ADCON0 = 0x81;
	ADCON1 = 0xC4;
        while(1)
	{
		__delay_us(100);
		ADCON0bits.GO = 1; //Start Conversion
		while(ADCON0bits.GO == 1);	//Wait Here for End of COnversion
		adc_data = ADRESH & 0x00FF;
		adc_data = adc_data<<8;
		adc_data = adc_data | ADRESL;
		
		ADCON0 = 0x80;	//A/D Feature is Powered-OFF
		/************************************************
		Time to Start Second Timer located at AN1
		**************************************************/
		__delay_ms(20);
		ADCON0 = 0x89;
		ADCON0bits.GO = 1;	//Start Conversion
		while(ADCON0bits.GO == 1);	//Wait Here for the End of Conversion
		adc_phase_data = ADRESH & 0x00FF;
		adc_phase_data = adc_phase_data<<8;
		adc_phase_data = adc_phase_data | ADRESL;
		ADCON0 = 0x80;	//A/D Feature is Powered-OFF

		/*****************************************
		SWITCH BACK to First Analog Channel
		******************************************/
		ADCON0 = 0x81;
		__delay_ms(20);
	}

Can any one help me regarding this...

 

[hamed8419215]

hi
1- in your code there is not any delay for charging S/H capacitor on second channel.
i think that you inserted "__delay_ms(20);" for this, but you should
insert delay after selecting a channel (not before it).
2- don't set ADON bit and GO/DONE bit in same instruction. first set ADON and then
set GO/DONE (after some time to charging S/H).
3- there is no need to turn off AD to changing channels, you can change channel while
the AD is on.
4- 20ms delay is not needed for charging S/H capacitor.
5- try this code:

ADCON0 = 0x81;
ADCON1 = 0xC4;
while(1)
{
//__delay_us(100);
ADCON0bits.GO = 1; //Start Conversion
while(ADCON0bits.GO == 1); //Wait Here for End of COnversion
adc_data = ADRESH & 0x00FF;
adc_data = adc_data<<8;
adc_data = adc_data | ADRESL;

//ADCON0 = 0x80; //A/D Feature is Powered-OFF
/************************************************
Time to Start Second Timer located at AN1
**************************************************/
ADCON0 = 0x89;
__delay_ms(20);
ADCON0bits.GO = 1; //Start Conversion
while(ADCON0bits.GO == 1); //Wait Here for the End of Conversion
adc_phase_data = ADRESH & 0x00FF;
adc_phase_data = adc_phase_data<<8;
adc_phase_data = adc_phase_data | ADRESL;
//ADCON0 = 0x80; //A/D Feature is Powered-OFF

/*****************************************
SWITCH BACK to First Analog Channel
******************************************/
ADCON0 = 0x81;
__delay_ms(20);
}