ADC on PIC24FJ256GA705

[nazoa]

Hello,

I'm having problems getting the ADC to work on a PIC24FJ256GA705 chip.
I have the following simple code.

#DEVICE ADC=10

Then in my main code, the ADC is set up as follows.

setup_adc_ports(sAN10, VSS_VDD); //Use pin C0 as analog input
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel(10);

Then, a routine to read the ADC is as follows:

int16 R;
R=read_adc(adc_start_and_read);

The problem is that an ADC value is never returned. The thing times out.
Any suggesstions?
Thanks

[temtronic]

You really need to post a short, complete program that others can copy/compile/test.

[Ttelmah]

and (critical), what compiler version?????.

There were issues with several things on this family around 5.080, so the
version is very important.
Also, use the correct case for the ADC_START_AND_READ define. Though
this should not matter in the default setup with case significance turned off,
it is always better to use upper case for defines, since his helps to tell
everyone that it is a define.

[Ttelmah]

A couple of other comments:

First the high speed ADC on chips like this has a much lower input impedance
requirement than the standard old PIC ADC. How are you feeding this?. It
really needs to be fed by an op-amp, not from any form of resistive
divider.
Second, these ADC's are differential. You can specify Vss as the second
input, but this does need to be specified.

Also (just added), one other critical thing. You cannot use the internal RC as you show!. You have to use this divided by two. The clock rate of the
internal RC, is faster than the ADC supports. From the data sheet: