Parallel and Series Comunication

Microprocessor System and Applications

Assignment 3

a)

Serial communication is the transmission of data, on bit at a time. Computers transmit data in terms of bytes, with each bit being made up of eight bits. A bit is characterised as either a logical 1 or 0. Serial ports are used to convert each byte into bits, and therefore a line of 1 s and 0 s. As well as being used to convert lines of 1 s and 0 s into bytes. An electronic chip called a universal asynchronous receiver/transmitter, UART, in the serial port is used to make the translations.

The serial port has 25 pins, 22 of which are used signals and ground, these are shown in the diagram below:

I will explain the transmit and receive pins first, whenever the serial port sends a logic one, 1, a negative voltage occurs on the transmit pin. When a logical zero, 0, is sent from the serial port, a negative voltage occurs, and when there is no date being sent from the serial, the transmit port is negative, 1, and is at a MARK state. Also, the serial port is able to keep the transmit pin at a positive voltage, 0, this is known as a SPACE or BREAK state.

When the serial port, UART, transmits a byte, it initially sends a ‘start bit’, this has a positive voltage, 0, and this is then followed by the data, in the form of 8 bits generally. This is then followed by one or two ‘stop bits’, which are negative, 1, voltages. This process is then repeated for each byte sent. The diagram below illustrates what how a byte transmission works: