ADC problems with C library and new code

Technical Programming
1

Has anyone successfuly manipulated the ADC hardware directly? It appears that the C compiler function “SetChanADC()” doesn’t work correctly. I have tried to set the channel manually but can’t seem to get it to work correctly.

The PIC (and IFI) defines show the channel # shifted left three bits, but the 18F8520 data sheet shows them shifted only 2 bits. SetChanADC() doesn’t shift the bits at all.

OpenADC() does the right thing with the channel, but I don’t want the overhead…

Cheers!

2

It turns out there is a bug with SetChanADC() - you need to right shift the channel one bit. This is clearly a bug in the C library since the OpenADC() function works correctly with the standard channels.

So, do the ADCopen once in your init code, then you can write a lean:

unsigned int GetADC(unsigned char chan)
{
SetChanADC(chan>>1);
Delay10TCYx(5);
ConvertADC();
while(BusyADC());
return ReadADC();
}