On Sat, Apr 17, 2010 at 2:52 PM, mattschinkel <[email protected]>wrote:
> > > How may I use a 18F67J50 I/O pin that switches between input/output > with a 5v device (such as a hard disk)? > > Imagine that a 5V tolerant input is a VDD=3.3V input in series with a small resitor. That's the way things work, except that input resistor is a MOS driven transistor (maybe an NMOS+PMOS pair). When the IO act as an output, the drain-source impedance is low, when the IO acts as input, the drain-source impedance is high, so it limits the input current and through it away to the VDD via the input clamping diode. However, the 5V tolerant pins does not have anymore clamping diodes to VDD. You can only guess that, seeing that MCLR is a 5 V tolerant input and does not have clamping diode (if would have, programming would be impossible). Connecting the 5V tolerant pins as 5V logic outputs (no open drain but regular IOs) can be done only by manipulating the IO direction using LAT and TRIS registers, see the chapter "I/O Port Pin Capabilities/ Interfacing to a 5V System" from datasheet. Vasile -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
