Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
9 years, 7 months ago.
Need pullup resistors for I2C on LPC1768?
I thought I read something that said the LPC1768 doesn't need pullup resistors for I2C. Is this true? If so how do you use the API to to configure an I2C port without pullups?
If pullup resistors are needed for I2C on LPC1768 what value of resistors and what the circuit look like on the pins? And what about API configuration of the I2C port for when external pullups are used?
Thanks.
Question relating to:
1 Answer
9 years, 7 months ago.
Some i2c pins do have GPIOs that can configure internal pullup resistors, but the values are too high to use with i2c devices. You should use external pullups of values between 1K and 2.5K depending on loading and speed you are trying to operate at.
Resistor value depends on the I2C frequency and bus capacitance, you need to ensure signal rise time conform to spec. That said 2K2 works fine for me. The declaration I2C i2cport( SDA, SCL); configures it.
posted by Pramod Joglekar 08 Sep 2014Thank you for the help Pramod. I appreciate it.
posted by Jim Norton 08 Sep 2014