pic18f24k22 impossible to set an channel 16, 17, 18 ,19

[blo]

Hi, I'm using a pic18f24k22. When I use the set_adc_channel function it work great with all analog channels from an0 to an15, when I set a channel greater than 15 it doesn't work.
I've noticed that analog channel greater than 15 use 5 bit for setup the channel in the ADCON0 register.
How I can fix the problem?
Is it possible to modify function set_adc_channel?

I've pcwhd 4.120
thanks to all.

[PCM programmer]

Post a short but complete test program that shows your problem.
The program should look very similar to the one in the link below,
but modify it to show your problem:
http://www.ccsinfo.com/forum/viewtopic.php?t=44709&start=11

[blo]

The problem is that pcwhd has a bug in the setup_adc_ports() function that cannot permit the external positive voltage reference.
And it has another bug in the set_adc_channel() function that cannot permit you to set the 6th bit of the ADCON0 register. So it work fine between an0 and an15 channel, but cannot set greater channel of adc.
Now i set manually the two register and it works.

where i can find the set_adc_channel function so i can modify the function?

[PCM programmer]

CCS doesn't give the source code for that function.

[PCM programmer]