für ack muss sda low sein. für nack muss sda high sein.

Data is transferred between a Master and a Slave synchronously to SCL on the SDA line
on a byte-by-byte basis. Each data byte is 8 bits long. There is one SCL clock pulse for
each data bit with the MSB being transmitted first. An acknowledge bit follows each
transferred byte. Each bit is sampled during the high period of SCL; therefore, the SDA
line may be changed only during the low period of SCL and must be held stable during
the high period of SCL. A transition on the SDA line while SCL is high is interpreted as a
command (see START and STOP signals).

frage damit beantwortet?!?!