I2C pins question

[Coccoliso]

Hi,
default ports for I2C in FW PIC24 version are connected to RP3/RB3 (SDA line) and RP15/RB15 (SCL line).
These two ports are not 5V compatible but I guess I can do a 10K pull-up to 5V to connect a PCF8574 .. or burn everything ?
Someone has already tried?

[David John Barker]

PIC SDA and SCL lines are fixed in harware, they are not remappable. To maintain pin compatibility with Arduino, Firewing uses software I2C on pins which are not 5v compatible. That said, you can use the hardware pins located on the PIC using the HI2C library, which will provide 5v compatibility.

[David John Barker]

...I should add, a correctly implemented I2C bus should be open drain. In other words, pulling up to 3.3v (not 5.0v) will work for most 5.0v systems. This is because 3.3v is normally enough to be interpreted as logic high. In summary, pull to 3.3v and not 5.0v between Firewing and 5.0v peripheral.

This means you will be fine using software I2C library mapped to default Arduino compatible pins.