CAD 3 channels

[robertop]

hi people:

I have a problem, I need use 3 channel but I can't did that. But I can used one channel, I Have pic 16f877 : but I need your help: my code is:

#if defined(__PCM__)
#include <16F877.h>
#fuses XT,NOWDT,NOPROTECT,NOLVP
#use delay(clock=4000000)
#byte puertab=0x06

void main() { //
int value0,value1,value2;
set_tris_b(0x00);
setup_adc_ports(ALL_ANALOG);
setup_adc( ADC_CLOCK_INTERNAL );
// set_adc_channel( 1 );


do {
set_adc_channel(0);
value0 = Read_ADC();
puertab=value0;
delay_ms(500);

set_adc_channel(1);
value1 = Read_ADC();
puertab=value1;
delay_ms(500);

set_adc_channel(2);
value2 = Read_ADC();
puertab=value2;
delay_ms(500);

} while (TRUE);
}


please helpme !!

bye and thank u.

[Haplo]

Two things:

1. From PIC16F877 datasheet: "When the device frequencies are greater than 1 MHz, the internal RC A/D conversion clock source is only recommended for SLEEP operation.". So for a 4MHz crystal it is recommended to use setup_adc(ADC_CLOCK_DIV_8).

2. From the CCS help file on set_adc_channel(): "Be aware that you must wait a short time after changing the channel before you can get a valid read. The time varies depending on the impedance of the input source. In general 10us is good for most applications.". You need to add that delay everytime you change the ADC channel, something like this:

[rwyoung]

Another "good" way to delay is to make a dummy read of the new channel.