All the protocols that we analyze in this chapter manage the access to a serial bus, which may consist of one or more wires, transporting the information in the form of electrical signals corresponding to logic levels, zeros and ones, when associated with specific time intervals. The protocols are different in the way they transmit and receive information on the data bus lines. To transmit a byte, the transceiver encodes it as a bit sequence, which is synchronized with a clock. The logic values of the bit are interpreted by the receiver reading its value on a specific front of the clock, depending on the clock's polarity.
Each protocol specifies the polarity of the clock and the bit order required to transmit the data, which can start with either the most or the least significant bit. For example, a system transmitting the ASCII character D over a serial line regulated by raising clock fronts, with most significant bit first, would produce a signal like the...