31.2.5.1.3 Bus Collision During a Stop Condition

Bus collision occurs during a Stop condition if:

  1. After the SDA pin has been deasserted and allowed to float high, SDA is sampled low after the BRG has timed out (see Figure 31-39).
  2. After the SCL pin is deasserted, SCL is sampled low before SDA goes high (see Figure 31-40).

The Stop condition begins with SDA asserted low. When SDA is sampled low, the SCL pin is allowed to float. When the pin is sampled high (clock arbitration), the Baud Rate Generator is loaded with SSPxADD and counts down to zero. After the BRG times out, SDA is sampled. If SDA is sampled low, a bus collision has occurred. This is due to another host attempting to drive a data ‘0’ (see Figure 31-39). If the SCL pin is sampled low before SDA is allowed to float high, a bus collision occurs. This is another case of another host attempting to drive a data ‘0’ (Figure 31-40).

Figure 31-39. Bus Collision During a Stop Condition (Case 1)
Figure 31-40. Bus Collision During a Stop Condition (Case 2)