Hi Guys,
I have a 5 Volt pic 16F628A, and a 3.3 Volt dsPic33FJ64GP802,
and want to connect both chip’s UART tx and rx pins together for communication between the two pics.

It seems to me so far that I can just directly connect each chip’s tx pin to the other chip’s rx pin.

Is it really this easy without any level shifting at all, or am I missing some information?
The 3.3 Volt dsPic has some 5 Volt tolerant pins.
Cheers, Art.

Pic 16F628A (4.5-5.5V)

Input  low voltage Min: VSS - Max: 0.8V
Input high voltage Min:2.0V - Max: VDD(5V).

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dsPic 33FJ64GP802 (3.0-3.6V)

Input  low voltage Min: VSS - Max: 0.2V
Input high voltage Min: 0.7 - Max: 5.5V
(on a 5 Volt tolerant I/O pin)

 

hi Art,
Providing the Input pins on the PIC33 are 5V tolerant there should be no problem.
On a Neo GPS input I used a simple resistive divider, 5v down to 3v.
Look at Tip #5 on this PDF for other options.
E

 

Hi Eric, Yes I have that document, and know about level shifting, but I think I should not need it altogether.
resistive divider is the slowest way, though I think at serial speeds it wouldn’t hurt,
but I should need nothing at all.

There is a consideration in the dsPic datasheet about total current being sent in all IO pins collectively,
where the voltage is above the dsPic VDD, but this is only for one pin.

 

If you need to level shift, here are some links you may find useful:

Microchip:
http://ww1.microchip.com/downloads/en/DeviceDoc/chapter 8.pdf

TI:
http://www.ti.com/lit/sg/scyb018f/scyb018f.pdf

Philips (secondary site):
http://www.adafruit.com/datasheets/an97055.pdf

Sparkfun board and schematic:
https://learn.sparkfun.com/tutorials/bi-directional-logic-level-converter-hookup-guide

John

 

Yes, but the whole idea is I think I do not need to in this case.. to save hardware.
I think it should just be the two wires.