Question on Schmitt Trigger input with a 3.3V Serial device

[khufumen]

I'm sending serial data from a small GPS unit running at 3.3V to port C4 on a PIC18F458
running at 5V. After much hair pulling I realized the Schmitt trigger required (.8 * 5) 4V to signal
an 'on' state which of course it wasn't getting.

My question is:

is there an IC chip that can boost my serial output from the GPS unit to
5 volts so that it can be read on port C4?

In the past I've used Max232s to convert from TTL levels
to 12V/-12V levels but I don't need to invert. I just want to bump up the serial voltage levels
between the the GPS unit and the PIC. I realize I can simply move the input to a TTL port on the PIC
but I need to use port C4. I also don't want to lower VDD on the PIC since I am also running AD
conversions on some 5V sensors. Any input would be greatly appreciated.

Kind Regards
Eric

[rsocor01]

Hi,

You will need to use a level voltage converter to step up the serial signal from 3.3 to 5.0V. Of course that would be an extra component in your circuit. Can you run the GPS at 5V?

Robert

[khufumen]

Unfortunately, the GPS unit can't use 5 volts. I found a chip from On Semi Conductor, MC74VHC1GT,
which looks like it will do the trick.

Strange thing I noticed:
I have an Atmel AT45 memory chip connected to PortD (D0,D1,D2,D3) and it works fine. This is
weird because PORTD is all schmitt triggers as well in I/O mode and the Atmel memory chip runs at 3.3V. It
shouldn't work but it does [scratching my head]

[Gusse]

Hi khufumen,

Check AN10441 (http://www.nxp.com/documents/application_note/AN10441.pdf) application note, page 4, Fig. 1.

BR,
-Gusse-