The I2C bus needs pull up resistors.
I looked at the Arduino Due schematics and saw that there are pull up resistors RN5A (1K5) and RN5B (1K5) for the I2C pins 20 (SDA0-3), 21 (SCL0-3).
pin 20 (SDA0-3) = TWD1
pin 21 (SCL0-3) = TXCK1
My first question:
Is it true that I do not need additional pull up resistors if I connect an I2C slave to pins 20 (SDA0-3), 21 (SCL0-3) of the Arduino Due? (On the Arduino Due schematics it is noted as “I2C Voltage Translator”.)
My second question:
If I use the Wire-Library the I2C communication is via pins 20 and 21 ?
My third question:
How do I do (which library) I2C communication via pins 9 (SDA1 = TWD0) and 10 (SCL1 = TWCK0) ? There are no pull up resistors for pin 9 and 10?