22.2.4.1 Acknowledge (ACK)

When a host or client device in the serial chain sends a Start bit, the client must provide an Acknowledge of the Start. If multiple clients are in a chain and connected to the host, the host sends a Start, the last client in the chain sends an Acknowledge and a Start and then the next client sends an Acknowledge and Start; this continues until the first client sends an Acknowledge and a Start.