Parallel communications have a wide data bus, typically 8 bits or more. The data bits are sent out together in conjunction with a clock and control signal and these interfaces require high pin counts, depending on the width of the data bus. Serial data refers to transmitting each bit one after the other over a single wire. These interfaces require low pin counts, since only one pin is required to transmit or receive data. This course covers very low data rate interfaces used in microcontrollers. The serial interfaces in these systems are asynchronous (clock is not sourced with the data) or synchronous (clock is sourced with the data). As can be seen from the diagram, the synchronous serial interface provides a clock with the data. The transmitter drives data out the pin on one edge of the clock and the receiver latches data on the following edge.