PIC16F913 ADC issues (CCS version: 3.219)

Ben Dinsdale · Joined: 10 Aug 2007 Posts: 6 Location: East Yorkshire, UK

Hello, I'm having bother getting the ADC to work the circuit is very simple i'm using AN0 (pin 2) which is connected across a 1 Ohm resistor as shunt. I'm getting 0.5V at the PIN, but ca't get a reading from the ADC. which I'm monitoring using MPLAB ICD2. via the watch window.

I'm wondering if I'm missing somthing?

in the .h file I have added #device ADC=10

the ADC is set up as follows:

setup_port_a(sAN0 | VSS_VDD);
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel(0);

then I try to get the value using:

value = read_ADC();

where value is declared as a long

any help or suggestions will be greatly received

Thanks, Regards, Ben

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I don't have a 16F913, but I do have a 16F917, which is a very similar
chip. I was able to make it work.

I used a PicDem2-Plus board with the 16F917 plugged into it. I installed
your version of the compiler. I'm using an ICD2 with MPLAB vs. 7.41.
I used my voltmeter to adjust the trimpot for pin AN0 so it puts 0.5 volts
on that pin.

I used the test program shown below. In the Debugger menu, I went
to the "Select Tool" menu and picked "MPLAB ICD2". Then I compiled
the program and selected "Connect" in the Debugger menu. Then I
opened a Watch Window and set it up to watch the 'value' symbol.
Also, I did a right-click on the 'value' line and selected 'Properties' and
set it up to display the value in decimal (The default is Hex).
Initially the Watch Window says "out of scope". I put a breakpoint on
the delay_cycles(1) line in the source code. This is depicted with a little
red dot with a "B" in the middle of it, in MPLAB. Then I went to the
debugger window and selected "Run". It ran. It stopped on the
breakpoint and displayed this:

Gerhard · Joined: 30 Aug 2007 Posts: 144 Location: South Africa

Can you please explain the delay_cycles(1) in your program. I use delay_ms(20) before asigning the adc value to a variable.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Actually, it should be more like 20 us.

I really should have written the program like this:

Ben Dinsdale · Joined: 10 Aug 2007 Posts: 6 Location: East Yorkshire, UK

Thanks for the input guys,

I have solved the problem, I was having after alot of head scratching and going through the disassemby listing, and stacks. For some reason the read_ADC() wasn't polling the on bit ANCON0. So the value wasn't returned so I did the polling of ADCON0 manualy. its not ideal but it worked.

Thanks again guys

Regards Ben