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According to the Arduino pin Mapping
20 PB12 SDA 3 6
21 PB13 SCL 3 6
70 PA17 SDA1 3 6
71 PA18 SCL2 15 9
The first one seems pretty obvious, the second one though is confusing. They have different labels. I also do not see other SDA or SCL in the table. So is this a typo?
According to the Wire library documentation https://forum.arduino.cc/index.php?topic=132130.0:
The Arduino Due has two I2C / TWI interfaces SDA1 and SCL1 are near to the AREF pin and the additional one is on pins 20 and 21.
And the table:
Arduino Due: 20 (SDA), 21 (SCL), SDA1, SCL1
So it seems in your table SCL2 should be SCL1.
