If you send bits one at a time, you are using serial communication. If you send one extra bit for each 8 bits to make sure your data got there intact, it is called a parity bit. Bit parity can be odd or even. It is even, if you assign 0 to the parity bit when the sum of the 8 bits is a even number. In this case, you assign 1 to the parity bit when the sum is an odd number. The parity is odd, if the logics is reversed. After the byte has arrived, the system will sum 8 bits and check if it matches the even-or-oddness predicted by the parity bit.
Two common connector type are used for serial communication: the 9-pin connector DB9 and (less often) 25-pin DB25 connector, which is essentially the same. A serial port male connector looks like this:
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\ o o o o o o /
\ o o o o o o /
\ o o o o /
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The heart of the serial communication technology is the UART (Universal Asynchronous Receiver/Transmitter), which converts parallel streams of data into a single sequence. As soon as the CPU sends the bits to the UART, it is free for another job, and the UART will convert the data into a single sequence and send the bits one at a time over the serial cable using the internal clock to define the time interval for the next bit to be sent. The UART will also send the start bit, the stop bit, and the parity bit (if necessary).
Modern PCs can exchange data over the serial port at rates up to 115 KB/s, but this will translate into a maximum data rate of about only 11.5 KB/s without parity and 10.5 KB/s with parity due to the serial communication protocol overhead.
You will be able to read more about serial interface in this place(Uma das fontes deste material): IEEE (Institute of Electrical and Electronic Engineers) .
"IEEE, pronounced "Eye-triple-E," stands for the Institute of Electrical and Electronics Engineers. The association is chartered under this name and it is the full legal name. However, as the world's largest technical professional association, IEEE's membership has long been composed of engineers, scientists, and allied professionals. These include computer scientists, software developers, information technology professionals, physicists, medical doctors, and many others in addition to IEEE's electrical and electronics engineering core. For this reason the organization no longer goes by the full name, except on legal business documents, and is referred to simply as IEEE.
The IEEE is dedicated to advancing technological innovation and excellence. It has about 425,000 members in about 160 countries, slightly less than half of whom reside in the United States." Wikipedia
"O Instituto de Engenheiros Eletricistas e Eletrônicos ou IEEE (pronuncia-se I-3-E, ou, conforme a pronúncia inglesa, eye-triple-e) é uma organização profissional sem fins lucrativos, fundada nos Estados Unidos. É a maior (em número de sócios) organização profissional do mundo. O IEEE foi formado em 1963 pela fusão do Instituto de Engenheiros de Rádio (IRE) com o Instituto Americano de Engenheiros Eletricistas (AIEE). O IEEE tem filiais em muitas partes do mundo, sendo seus sócios engenheiros eletricistas, engenheiros da computação, cientistas da computação, profissionais de telecomunicações etc. Sua meta é promover conhecimento no campo da engenharia elétrica, eletrônica e computação. Um de seus papéis mais importantes é o estabelecimento de padrões para formatos de computadores e dispositivos." Wikipedia
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