Greetings,

I have used the great piclist resources and archive to get myself going on
several pic projects, but this is my first post to the mailing list. 
Thanks to everyone for their contributions to this resource.

I am trying to interface the Usart of a PIC16F628 to another device that
runs at 3.3 volts.

One solutions seems to be to run the PIC at 3.3 volts. The datasheet for
the 16F628 gives the power requirements as "flexible", between 2 and 5
volts.  The datasheet also has a graph of speed vs voltage, suggesting
that I should not try to exceed 4 MHz at 3 volts.  I have always worked at
5v, so I wrote a simple LED blinking program to test the pic at 3.3 volts.
 I used the same oscillator as always (a 3.579545MHz crystal with 2 22pF
capacitors).  The program works great at 5 volts, but I get nothing at
3.3volts. Does anyone have experience working with PICs under 5 volts?  Is
there something obvious I have missed?

Another solution would be a bridge of some sort.   This is indeed what I
did during prototyping: the pic's 5v Usart was connected to MAX202 which
was connected to a MAX3222 with in turn was connected to the 3.3v logic of
a smart dust module I am working with.  Does anyone know of a better way
to bridge the logic levels?  Is there a MAX202-like IC that bridges 3.3 &
5 volt logic - or a simpler solution?

Thanks for all the great resources, and thanks in advance for any sugestions.

Cheers,

Ian

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