Pic is PIC18F252. Dave McGuire escribió: > On Mar 8, 2007, at 10:21 AM, Markos wrote: > >> The datasheet does not mention anything about the voltage >> reference max input voltage. If you see in "electrical >> characteristic", >> states that you cannot operate the device above 0.8V over VDD in IO >> pins: >> >> VIH Input High Voltage >> I/O ports: >> D040 with TTL buffer 0.25 VDD + 0.8V >> >> Thats all i've found about it, because in the ADC chapter doesn't >> mention anything about it. >> > > Microchip (almost?) always lists an allowable range for the > external Vref input in the datasheets. > > Which PIC chip are you using? > > >> So, to summarize it, If I divide the voltage, I loose resolution >> (inverse proportional). Same applies to the Op Amp, which will reduce >> the voltage too, but with higher part count and cost ;-) >> > > ...and accuracy, and input impedance. OpAmps are hardly expensive > these days. > > -Dave > >
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