In I3C v1.1, Table 10 (I3C Open Draining Timing parameters) lists the tHigh symbol as having a maximum value of 41 ns, and then Note 4 says that “tHigh may be exceeded when the signals can be safely seen by I2C Slaves”. This means that a 41 ns tHigh will ensure that no legacy I2C Slave will see the SCL changes, and so will not interpret the START followed by the Address phase nor the ACK/NACK. The Master may use a much longer tHigh if there is no harm with a legacy I2C Slave on the I3C Bus seeing the clocks. For example, the legacy Slaves will see the STOP and then a START. It is acceptable for them to see the Address that follows (arbitrated or not), since none of those Addresses will match their own Address. However, as the tLow may well be 200 ns, this may present problems for any legacy I2C slaves not fast enough to correctly handle a 200 ns Low period.

FAQ Type: 
I3C