In the I3C v1.1 specification, Table 110 I3C Open Draining Timing Parameters shows the tHigh symbol maximum value as 41 ns, and Note 4 states “tHigh may be exceeded when the signals can be safely seen by I2C Targets”. This means that a 41 ns tHigh will ensure that no Legacy I2C Target will see the SCL changes, and so no Legacy I2C Target will interpret the START followed by the Address phase nor the ACK/NACK. If there is no harm with a Legacy I2C Target on the I3C Bus seeing the clocks, then the Controller may use a much longer tHigh. For example, Legacy I2C Targets 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 Targets not fast enough to correctly handle a 200 ns Low period.
In the I3C v1.1.1 specification, the parameters are defined in the equivalent Table 122. In the I3C Basic v1.1.1 specification, the parameters are defined in the equivalent Table 86.