During a Start condition, a bus collision occurs if:
During a Start condition, both the SDA and the SCL pins are monitored.
If the SDA pin is already low, or the SCL pin is already low, then all of the following occur:
The Start condition begins with the SDA and SCL pins deasserted. When the SDA pin is sampled high, the Baud Rate Generator is loaded and counts down. If the SCL pin is sampled low while SDA is high, a bus collision occurs because it is assumed that another master is attempting to drive a data ‘1
’ during the Start condition.
0
)
If the SDA pin is sampled low during this count, the BRG is reset and the SDA line is asserted early (Figure 3). If, however, a ‘1
’ is sampled on the SDA pin, the SDA pin is asserted low at the end of the BRG count. The Baud Rate Generator is then reloaded and counts down to zero; if the SCL pin is sampled as ‘0
’ during this time, a bus collision does not occur. At the end of the BRG count, the SCL pin is asserted low.