There are only two ways to connect external devices to the machine, one is parallel and the other is serial. A parallel connection transmits multiple data streams at the same time through multiple channels; a serial connection transmits only one data stream at the same time.
Parallel
Parallel refers to the transmission of multi-bit data through parallel lines at the same time. In this way, the data transmission speed is greatly improved, but the length of the parallel transmission line is limited. Because the length increases, the interference will increase and the data will be prone to errors.
Classification
Terminals communicate with other devices (such as other terminals, computers, and external devices) through data transmission. In data communication, according to the number of data bits transmitted each time, communication methods can be divided into: parallel communication and serial communication.
In parallel communication, each bit of data is transmitted at the same time, and can be performed in parallel in units of words or bytes. Parallel communication is fast, but uses many communication lines and is costly, so it is not suitable for long-distance communication. Various internal buses of a computer or PLC transmit data in parallel.
Features
1. Each data bit is transmitted simultaneously, with fast transmission speed and high efficiency. It is mostly used in real-time and fast situations.
2. The most basic information exchange method in microcomputer systems.
3. Information transmitted in parallel does not require a fixed format.
4. The data transmission rate of the parallel interface is 8 times faster than the serial interface. The theoretical value of the data transmission rate of the standard parallel port is 1Mbps (megabits/second).
5. Parallel transmission The data width can be 1 to 128 bits, or even wider, but as many data lines are required as there are data bits, so the cost of transmission is high.
6. Parallel communication has poor anti-interference ability.
7. Data transmission within the integrated circuit chip, between components on the same plug-in board, and between plug-in boards in the same chassis are all in parallel.
8. Use the computer's word length, usually 8 bits, 16 bits or 32 bits as the transmission unit, to transmit one word length of data at a time.
9. Suitable for short-range, large-scale and fast information exchange between external devices and microcomputers.
10. Parallel data transmission is only suitable for short-range communication, usually the transmission distance is less than 30 meters.
Serial
Serial refers to transmitting one bit of data at a time and continuously on the computer bus or other data channels. Communication method for the above single process. It communicates on a serial port by transmitting several bits of data at a time. Serial communications are used for long-distance communications and in most computer networks, where cables and synchronization make practical use of parallel communications difficult.
With its improved signal integrity and propagation speed, serial communication buses are becoming more and more common, and their advantages have begun to surpass parallel buses even in short-distance applications that do not require serial serializer and solve shortcomings such as clock skew and interconnect density. The upgrade from PCI to PCI Express is one example.
Comparison
Communication between computers and between parts within a computer can occur in both serial and parallel ways. . A parallel connection carries multiple data streams at the same time through multiple channels (such as wires, printed circuit wiring, and fiber optics); a serial connection carries only one data stream at a time.
Although the serial connection can transmit less data in a single clock cycle than the parallel data, the former's transmission capability seems weaker than the latter, but the actual situation is often that serial communication can be compared to Parallel communication makes it easier to increase the communication clock frequency, thereby increasing the data transmission rate. There are some factors that allow serial communication to have higher communication clock frequencies:
There is no need to consider the clock skew of different channels;
Serial connections require less physical media, such as cables and optical fibers, than parallel communications, thus reducing the volume of space occupied;
The problem of crosstalk can be greatly magnitude relief.
In many cases, serial communication becomes the better choice due to its lower deployment cost, especially for long-distance transmission. Many integrated circuits have serial communication interfaces to reduce pin count and thereby save costs.
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