Serial port transmission is one bit, and parallel port can transmit multiple bits simultaneously. Details are as follows!
COM stands for serial port, LPT (not LTP) stands for parallel port. Serial port is a port provided by computer bus for data transmission. In the serial port, data is streamed bit by bit, and LPT is another transmission port. Generally, it is byte stream here, that is to say, the serial port is like a row of transmission in each queue, and the parallel port is 8-bit parallel transmission, although it feels that LPT is 8 times that of the serial port. However, due to baud rate, serial port is not necessarily slower than parallel port. Baud rate refers to how many bits of data are transmitted per second. Here Porter is a bit, not a byte (1 byte = 7 bits+1 bit check). If there is such a serial port, its baud rate is 100bit/s and baud rate is 80bit/s, which means that this serial port can transmit 1 00 bit at1s, and the parallel port can transmit 80bit per second, transmitting 10 times, but it is 65448.
serial interface
Serial interface, COM interface for short, is an extended interface using serial communication protocol. The serial port appears around 1980, and the data transmission rate is115 kbps to 230 kbps. Serial port is generally used to connect mouse and external modem, old camera and tablet. At present, some new motherboards have begun to cancel this interface.
parallel interface
Parallel interface, LPT interface for short, is an extended interface using parallel communication protocol. The data transmission rate of parallel port is 8 times faster than that of serial port, and the data transmission rate of standard parallel port is 1Mbps, which is generally used to connect printers and scanners. So the parallel port is also called the printing port.
In addition, both serial port and parallel port can be interconnected by direct cable connection, in which data can only be transmitted at low speed. The function and structure of serial port and parallel port of PC have not changed for many years. When using serial-parallel ports, in principle, each peripheral must insert an interface. If all interfaces are used, you can only add interfaces by adding cards. Serial port and parallel port are not only limited in speed, but also inconvenient to use, such as not supporting hot plug. With the popularization of USB interface, it is rarely used at present, and it will be eliminated with the promotion of BTX specification.
Where there are serial ports and parallel ports on the computer, there should be: hard disk, motherboard, printer. Serial ports are generally used to connect some special external devices. Such as communication equipment. Parallel ports are usually used to connect printing devices. The serial port is relatively small, and there are prominent needles exposed. Parallel port is generally larger than serial port, generally red, with two rows of holes.
A serial port is described as one channel, while a parallel port has eight channels.
It can transmit 8 bits (one byte) data at the same time.
But the speed of parallel port is not fast, because 8-bit channels interfere with each other. Transmission is limited by speed. Moreover, when transmission errors occur, 8-bit data should be retransmitted at the same time. The serial port has no interference. Just resend one bit after transmission error. So fast is faster than parallel port. This is the importance people attach to the serial hard disk.
Parallel pin function list
Pin function pin function
1 strobe, active low 10 confirmation, active low.
2 data channel 0 1 1 busy
3 Data channel 1 12 is out of paper.
4 data channel 2 13 selection
5 Data channel 3 14 automatically stops, and the low level is effective.
6 Data channel 4 15 error, active low.
7 data channel 5 16 initialization, low level effective.
8 data channel 6 17 select input, active low.
9 data channel 7 18 to 25 ground wire
25-pin serial port function list
Pin function pin function
1 empty 1 1 empty
2 sending data 12 to 17 is empty.
3 The received data 18 is empty.
4 Send request 19 is empty.
5 Send Clear 20 Data Terminal Ready to Complete
6 Data preparation completed 2 1 empty
7 signal grounding 22 ringing indication
8 Carrier detection 23 to 24 is invalid.
9 empty, 25 empty
10 is empty
9-pin serial port function list
Pin function pin function
1 carrier detection 6 data ready.
2 send data 7 send request
3 Receiving Data 8 Sending Clear
4 The data terminal is ready to complete 9 ringing instructions.
5 Signal ground wire
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Comparison between serial port and parallel port
serial interface
Serial port is usually referred to as serial port for short, and English logo is serial or COM；; Nowadays, PC computers generally have two serial ports, COM 1 and COM 2. These two interfaces are the standard interfaces that first appeared in computers, that is, RS232 standard. Before this standard came into being, computer peripherals produced by various manufacturers were also produced together with computers, which were incompatible with peripherals from other manufacturers. RS232 standard is too slow. Now the remaining two interfaces are used for square mouse and external "cat" respectively. Serial port is different from parallel port, and its data and control information are transmitted one by one. Although the speed will be slower, the transmission distance is longer than the parallel port. Generally, COM 1 uses a 9-pin D connector, and COM 2 uses an old-fashioned DB25-pin connector.
Interfaces are divided into asynchronous interfaces and asynchronous interfaces. In order to let the receiver know that new data has appeared on the data line, it is most convenient to use the synchronization signal. The advantage of synchronous communication is that it can use any frequency allowed by the line, but it is not convenient in practical use, so asynchronous communication is mostly used in serial communication now. The earliest serial interface RS232 is an asynchronous communication protocol. Asynchronous communication needs to coordinate the frequencies of both parties, which is called handshake. Whether we use 28, 36 or 56K cats, we can connect to the same access address, because a series of "beep" sounds after dialing, that is, shaking hands, coordinate the communication frequencies of both parties.
parallel interface
Parallel interface is also referred to as parallel port for short, and is identified as parallel or LPT and PRN in English. At present, the parallel port in the computer is mainly used as the printer port, instead of the 36-pin connector, the 25-pin D connector is used. The so-called "parallel" means that 8-bit data is transmitted through parallel lines at the same time, which greatly improves the data transmission speed, but the line length of parallel transmission is limited, because the length increases, the interference will increase and the data will be prone to errors. At present, there are five common parallel ports: 4-bit, 8-bit, half-8-bit, EPP and ECP. Most PCs are equipped with 4-bit or 8-bit parallel ports, and all computers supporting the IEEE 1284 parallel port specification are basically equipped with ECP parallel ports.
Standard parallel ports refer to 4-bit, 8-bit and half-8-bit parallel ports. The 4-bit port can only input 4-bit data at a time, but can output 8-bit data; The 8-bit port can input and output 8-bit data at a time. EPP port (enhanced parallel port) is developed by Intel and other companies, which allows 8-bit bidirectional data transmission and can be connected to various non-printer devices, such as scanners, LAN adapters, disk drives, CD-ROMs, etc. ECP (extended parallel port) is developed by Microsoft and HP, which can support command cycle, data cycle and multi-logical device addressing, and can use MA (direct memory access) in multi-task environment. At present, almost all motherboards above Pentium level have integrated parallel ports, which are marked as PAR-ALL 1 or LPT 1. This is a 25-pin double-pin socket.
Usb interface
USB is a "universal serial bus", and its Chinese name is universal serial bus. This is a new interface technology widely used in PC field in recent two years. Theoretically, USB technology consists of three parts: PC system with USB interface, software that can support USB system and devices that use USB interface.
There are two different connectors for USB devices, called A series and B series. Series A connectors are mainly designed for devices that need cables to maintain permanent connection, such as hubs, keyboards and mice. The USB interfaces on most motherboards are series A connectors. B series connectors are specially designed for devices that require detachable cables. Such as printers, scanners, modems, etc. The physical USB plug is a small rectangle.
Theoretically, USB can connect 127 devices in series, but in practical application test, it may not be enough to connect 3 ~ 4 devices in series. Moreover, as the USB product itself, only the keyboard has the dual-head design of input and output, and other products have only one input interface, so it is impossible to connect another USB device. At this time, if you need to connect multiple USB devices, you need a connection bridge-USB HUB, but the number of serial USB HUBs cannot exceed three, that is, you can't connect the USB hub to the third serial USB interface. At present, ATX motherboards generally only have two built-in USB interfaces.
Nowadays, USB has been applied to various peripherals of PC. Output devices, including scanners, digital cameras, digital video cameras, audio systems, monitors, etc. , mainly using the high-speed data transmission ability of USB. In terms of input devices, USB keyboard, mouse and joystick are extremely stable, and there are few problems. In addition, there are USB "cat" of DSL, USB ZIP drive of IOMEGA and USB PC network card of eTek.