1.1.3 ‘Read’ Signal

A ‘Read’ signal is shown in the figure below. The host pulls the bus low for 1 to 15 μs. Then, the target holds the bus low if it wants to send a ‘0’. If it wants to send a ‘1’, it simply releases the line. The bus should be sampled 15 μs after the bus was pulled low. As seen from the host’s side, the ‘Read’ signal is a ‘Write 1’ signal. It is the internal state of the target, rather than the signal itself that dictates whether it is a ‘Write 1’ or ‘Read’ signal.