Connected protection resistors and diferents voltages I/O Ports.

[AndJuan]

Hello all,

Two question ¿?

Based on curse 28 Pines (Arduino) I'm designing for PIC.
The PIC 18F26K22 in RB6-PGC (pin27) and RB7-PGD (pin28) ports are pin ICSP but I also want them used for I / O ports.

The question is have to put resistors in series. or as you would have t
o put?
as you do in ATMEGA16U2 / PIN15 (CLK) for ICSP1. (view picture).



Other polemic question is when...
I also want to add on the board an SPI display but this will PIC works 5V and LCD 3.3V, How to connect at different I/O ports (SDI, CLK, SC, A0, RST) if there are differents voltages.


THX.

[AndJuan]

[robertferanec]

Hello AndJuan

1) If these pins will work as clock outputs, you can put there 22OHM resistors. The 22R resistance is small and will not influence GPIO functionality of the pins. In any case, you can always replace them by 0R if needed.

2) You have more options. The simplest option is to use a buffer with 5V tolerant inputs (e.g. SN74LVC1G08DCKR). For example, have a look how we have connected a CAN transceiver in our OpenRex schematic (page 23, chip U19): http://www.imx6rex.com/wp-content/up...Production.pdf

Note: In case you are connecting bidirectional interfaces running on different voltages, you will need to use a bidirectional buffer. Here is example for something bigger 74LVXC3245.