transmissão para uma porta série

Serial and Parallel Port


#Serial #Parallel #Port

  • What are the input / output ports

  • Serial Port

  • Parallel Port

What are the input / output ports

At entry / exit door they are material elements of the computer that allow the system to communicate with external elements, that is, that it can exchange data, hence its name as an input / output interface (sometimes called an I / O interface).

Serial Port

At serial ports (also called RS-232, the name of the standard they refer to) represent the first interfaces that allowed computers to exchange information with peripherals. The term serial designates a data transmission over a single wire: the bits are sent one after the other (see the section on data transmission for a theoretical course on transmission modes):

transmission to a serial port


In the beginning, serial ports only allowed data to be sent, but they could not receive it. For this reason, bidirectional ports (like those of current computers) have two wires to carry out both sending and receiving data.

Serial communication is done asynchronously, which means that no synchronization signal (called a clock) is necessary, that is, data can be sent at arbitrary time intervals. On the other hand, the peripheral must be able to distinguish the characters (a character is 8 bits long) from the bit sequence sent to it.

This is the reason why, in this type of transmission, each character is preceded by a start bit (called the START bit) and an end bit (STOP bit). These control bits, necessary for a serial transmission, waste 20% of the band (for 10 bits sent, 8 are used to encode the character and 2 are used to guarantee reception).

Serial ports are usually integrated with the motherboard, so there are connectors on the back of the case, connected to the motherboard by cables, allowing you to connect an external element. The serial connectors have 9 or 25 pins and are presented in the following form (respectively DB9 and DB25 connectors):

DB9 connecteur


DB25 connecteur


A personal computer generally has one to four serial ports.

Parallel Port

Parallel transmission consists of sending data simultaneously to several channels (wires). At parallel ports present in computers allow sending 8 bits (one byte) at the same time through 8 wires:

transmission to a parallel port


The first bidirectional parallel ports allowed to achieve speeds of approximately 2.4 Mb / s. However, improved parallel ports have been developed to achieve higher throughputs such as EPP port (Enhanced Paralel Port), which allows to achieve speeds of approximately 8 to 16 Mbps and the ECP port (Enhanced Capabilities Port), created by the partnership between Hewlett Packard and Microsoft. It resumes the characteristics of the EPP port by adding a ‘Plug and Play’ support, that is, it enables the computer to recognize the connected peripherals.

Parallel ports, like serial ports, are integrated into the motherboard. DB25 connectors allow you to connect an external element (a printer, for example):

DB25 connecteur

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