Hi,

I'm connecting a 3.3V-powered PIC to a 5V-powered PIC via the hardware =20
USARTs.  Currently I have these prototyped and working well with =20
bi-directional mosfet level converters as shown here...
http://www.nxp.com/documents/application_note/AN10441.pdf

However, I need to fit this in a small enclosure and PCB real-estate =20
is a problem once again.  I'm wondering if I can eliminate or at least =20
reduce the components for the logic-level converter.

In the 5V-->3.3V direction, the 3.3V RX input (PIC24) is 5V fault =20
tolerant, so I should be able to direct-connect that.

In the 3.3V-->5V direction, it seems the 5V RX1 input (18F24K22) is a =20
Schmitt trigger, and the electrical specs for that in the datasheet =20
are minimum input-High voltage of 0.8Vdd, so 4.0V, and thus the 3.3V =20
signal won't work.

So that brings the 6 components down to 3 (mosfet and 2 resistors), =20
but is there a better (smaller footprint) way, or something I'm =20
missing here that would let me direct-connect the other direction?

FWIW, I did find monolithic converters such as this, but it doesn't =20
save much space... http://www.nxp.com/documents/data_sheet/PCA9306.pdf

Cheers,
-Neil.



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