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Do PICs exhibit a voltage drop ocross their output or do they swing Vss to Vdd?

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JohnJohn20

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Hi. I am powering a 16F828A PIC off a 3.7 volt mobile phone battery. Does the output transistors have a voltage drop across them or do the outputs truely swing from Vdd to Vss?

The datasheet says "All other RA port pins have schmitt trigger input levels and full CMOS output drivers". Does that tell me what I want to know?

I do not really trust the accuracy of my $10 multimeter to give me a true answer here.

Thanks.
 

All CMOS drivers go rail to rail with no load and drop voltage with current. Using Ohm's Law on the incremental drop you can calculate the ESR of the drivers. Some of the better drivers are found in Atmel CPU"s with 25 Ohm drivers and others are as high as 100 Ohms and original CMOS > 300 Ohms.
 
Ta SunnySkyguy.

Does it actually say anywhere in the datasheet typical values for the ESR?

Actually, I made the effort and read in the datasheet that the minimum voltage out is Vdd - 0.7V @ 4.5V 2.5mA.

So I would guess that the ESR is 280Ω maximum. Sigh, that doesn't seem to help much.
 
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I think what you are looking for are the graphs in pages 70/71 **broken link removed**

they show the current vs output voltage
 

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