[PIC]: Trouble w/multiple AD inputs (F877) by Brian Reed .

I've been using one A/D input for months and have now expanded to 3. I must really have something goofy in my code, because the channels interact with each other. Normally I'd do more testing before asking here, but I'm going to try and run it at the SME robot competion this Saturday (near Pittsburgh), so I wanted to ask if my error is obvious... This is what use to work, with the ICD demo board and the pot on RA0: void AD_init(void) { OPTION = 0x87; // Set TMR0 prescaler, and 1:256 ADCON1 = 0x0E; // Left justify result, 1 analog channel } and unsigned char AD_RA0(void) { ADCON0 = 0x41; // Fosc/8, A/D enabled ADGO = 1; // Set the bit to start the conversion while (ADGO) // Wait for the conversion to complete continue; // return ADRESH; // Return the AD value (just the top 8 bits) } Problem is, now that I've taken ADCON1 to 0x02 (for 5 D/A inputs and 3 digital I/Os, with Vdd&Vss as Vref's), the output of AD_RA0() does not vary through the full range, and is greatly affected by input on RA1. Yipes! Only when I turn RA0 and RA1 all the way up do I get a full-scale A/D reading on RA0. Here's the current code - likely this has the problem ---> /// PICLIST: note the change in ADCON1 void AD_init(void) { OPTION = 0x87; // Set TMR0 prescaler, and 1:256 ADCON1 = 0x02; // Left justify result, 3 analog channels } /// PICLIST: note the only difference between AD_RAx() routines is ADCON0 unsigned char AD_RA1(void) { ADCON0 = 0x49; // Fosc/8, A/D enabled ADGO = 1; // Set the bit to start the conversion while (ADGO) // Wait for the conversion to complete continue; // //// could/should disable A/D here? (w/ADCON0) return ADRESH; // Return the AD value (just the top 8 bits) } unsigned char AD_RA2(void) { ADCON0 = 0x51; // Fosc/8, A/D enabled ADGO = 1; // Set the bit to start the conversion while (ADGO) // Wait for the conversion to complete continue; // //// could/should disable A/D here? (w/ADCON0) return ADRESH; // Return the AD value (just the top 8 bits) } while (1) { uctmp1 = AD_RA1(); // sensor uctmp2 = AD_RA2(); // sensor PORTC = AD_RA0(); // Turn on LEDs per POT on ICD demo board } Thanks, - Bri -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics