Inhaos mega core, Pullup resistor on I2C bus


First, I'd like to know if there is onboard pullup resistor on inhaos mega core for I2C bus,

I've heard many version and i need to know, So Maybe internal pullup resistor actived by wire.h library ?

Secundo, How calculate pullup resistor for I2C bus I've 3-4 slaves on the bus, my megacore work on 3.3V level (Megacore 3.3V, OLED SSD1306, 2x EEPROM 24LC256, GY-91)

Best regards Bertrand

1) You have the board; measure it. Or look at the schematic (if you can find it). Further the two-wire interface does indeed activate the internal pull-ups; you have the source code ;) 2) TI I2CBus Pullup Resistor Calculation (pdf). There are probably more references on the web; this was the first one that showed in google.

Hi Sterretje,

Thanks for your answer,

Mesure Resistor on a board seems to be simple,
But is there a way to do it for internal resistor?

I added 2 pullup 1kResistors on SDA/SCL,
Is it compatible if internal pullup are actived?
Does 1k resistor is a good value?
I read .pdf, but many tutorial advice 4.7k to 10k…?

Best regards

1 kOhm should be OK from a processor perspective. It will be in parallel with the internal pull-up. Note that I'm no longer an electronics engineer and rather follow the instructions and use the indicated values.

You can't measure the internal pull-up and there is no need. If you are curious, you can try the following.

With nothing connected to the pin, add a 10 kOhm pull-down resistor; it will form a voltage divider with the internal pull-up. Power the board up with a sketch that enables the internal pull-up. Measure the voltage,; I think that that will be somewhere in the region of 1 Volt.

Thanks Sterretje,

All seems to go right

Best regards