Problems reading a analog input port RE0 pic18F45j50

[sonny]

Hello everybody not sure what I'm doing wrong. I have a 11k pullup in that port and a connector comes and either sets the port to ground or to a voltage divider 1.7, VDD is 3.3V. The only one that is reading accurate is the gnd.

[Ttelmah]

You are not ever going to get/see 1.629.

The adc, returns an integer, not a 'float' value.....

Now you don't show one critical line. #device adc=xx
This specifies the output format used for the ADC. probably defaulting to =16, which will then give a left justified 16bit value.

Then you are telling the ADC to use Vref. What do you have connected to the Vref+ input?. Odds are nothing?. If so, no wonder you get an odd value....
Assuming you don't have an external reference available, and want to use the supply, you need VSS_VDD.

Use #device ADC=10
to get the standard 10bit output from the ADC

Your adc value will then be Vin/(Vdd/1024) (yes, 1024, not 1023).

Since you are setting TAD_MUL_0, there must be at least Tacq, between selecting the ADC channel and actually reading. Does your divider meet the impedance requirements of the ADC (section 21.1 - quote "The maximum recommended impedance for analog sources is 2.5 k)?.

[sonny]

Ttelmah
thanks for the response

on the VREF I actually want to use vdd as vref+ and vss as vref- not sure if I'm doing it right, when I put ground I do see 0
is when I'm having my voltage divider which is 11k both of them so I guess I'm over the recommended impedance.

if I want to use vdd and vss do I need to set them in the code or is the default value?

thanks

[Ttelmah]

setup_adc_ports(sAN5|VSS_VDD);

[sonny]

Ttelmah

got it to work thanks my friend