can Vref- as +1V?

[meera83]

i m using PIC16F877.. I choose to use two analog voltage as input signal..

in the setting, i need to use RA2 as Vref+ and RA3 as Vref-...
if the input voltage that i want to use is from 1-5V..

can i port the RA3(Vref-) with positive voltage? or Vref- must 0V or less than 0V???

 

[blueroomelectronics]

Vref- has to be 0V or higher
it also has to be at least 2.5V lower than Vref+
Vref+ must be VDD or lower.

So setting for 1V is fine if Vref+ is at least 3.5V

 

[meera83]

Vref- has to be 0V or higher
it also has to be at least 2.5V lower than Vref+
Vref+ must be VDD or lower.

So setting for 1V is fine if Vref+ is at least 3.5V

is it no method how many analog input, there is only one range value Vref+ and Vref- can be used for all the analog input?

 

[donniedj]

blueroom: you snuck up from underneath me! Damn this slow BAUD RATE (300) forum

Yes you may. Vref- does not imply a compulsory negative voltage. This goes for electronics in general.

In section 15 of datasheet, get familar with the Absolute Maximum Electrical ratings.

The overall foundation to remember:
"Voltage on any pin with respect to VSS (except VDD, MCLR. and RA4) ....................................... -0.3 V to (VDD + 0.3 V)"
Then go to table 15-12 and read the valid ranged for Vref+ and Vref-. Vref-(min) cannot be less than Vss - 0.3v (within the overall foundation), in short not less than 0.3v. Vref-(max) cannot be larger than (Vref+) - (2.0v), 2 volts less then Vref+.

 

[blueroomelectronics]

donniedj is right, 2V is the minimum not 2.5V

And yes it sets the upper and lower limits for all the analog inputs.