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.
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.