Was thinking today whether or not a Pic would function the same at say 3v3 or 5v if the PIC was stated in the datasheet to be able to be used in the range of 2v to 5.5v? So if I have a PIC16F684 can I power it at 3.3v and run it with other 3.3v components or must I use it at 5v and level shift?

Thanks for your responses.

 

Usually 0-0.8 volts is digital zero. 2.7 or 2.8 volts and above is digital one. There is also low voltage systems where 1.8 volts has a corresponding digital value. So. Your PIC is stated to work on voltages from 2 to 5.5 volts. I believe that when you power it with 3.3 volts, it will work with 3.3 volt devices. It most likely will work with most 5 volt devices too, but you will have to see on case by case basis.

 

You can use it over the range of voltages stated in the datasheet. There are a few things that might change - the maximum oscillator frequency, the supply current, the voltage reference and ADC resolution for instance. You need to check the datasheet for the resources you are using.

 

Sage advice there, check the datasheet.

 

If the data sheet says it will operate on supply voltages from 2.0 volts to 5.5 volts, then it will operate from 2.0 volts to 5.5 volts, and that includes 3.3 volts.

However, note Figure 15-1 on page 128: at 3.3 volts, the maximum oscillator frequency is reduced to 10 MHz, so it can only run half as fast as it can at 5.0 volts. Also, you should expect that the I/O pins will not be able to source or sink as much current at 3.3 volts as they can at 5.0 volts, though how much less is not spelled out very clearly in the data sheet.

 

If the data sheet says it will operate on supply voltages from 2.0 volts to 5.5 volts, then it will operate from 2.0 volts to 5.5 volts, and that includes 3.3 volts.

However, note Figure 15-1 on page 128: at 3.3 volts, the maximum oscillator frequency is reduced to 10 MHz, so it can only run half as fast as it can at 5.0 volts. Also, you should expect that the I/O pins will not be able to source or sink as much current at 3.3 volts as they can at 5.0 volts, though how much less is not spelled out very clearly in the data sheet.

Would that include using an external oscillator? I was wondering the same thing....so my 20 mhz external osc would now be limited to roughly 10 mhz? Sometimes I get confused in reading/ searching the datasheet and that is why I ask these questions here. Thank you so much for your help.

 

whether or not a Pic would function the same at say 3v3 or 5v

will depend on what you mean "the same". the datasheet laid out some pretty clear distinctions when running the chip at different voltage levels.

 

Would that include using an external oscillator?

Yes. If there were an exception for an external oscillator, they would say so.

I was wondering the same thing....so my 20 mhz external osc would now be limited to roughly 10 mhz?

Yes, except for the "roughly" part; the data sheet is clear that below 4.5 volts, the chip is not guaranteed to work at ANY clock rate higher than 10 MHz. Period.

Sometimes I get confused in reading/ searching the datasheet and that is why I ask these questions here.

In general, it's a good idea to assume that a data sheet says exactly what it means and means exactly what it says, barring typographical errors.

 

Thank you OBW0549. Thank you for your guidance.

 

You're welcome. Good luck with the project.