Differences between the serial port and the parallel port

COM means the serial port, while LPT (not the LTP) means the parallel port. The serial port is a port provided by the computer bus for data transmission. In the serial port, data is transmitted in a bitwise stream, LPT is another port for transmission. Here it is generally a byte stream transmission, that is to say, the serial port is like each queue for a row of transmission, and the parallel port is 8-bit and arranged together for transmission, although LPT is eight times the serial port, the serial port is not necessarily slower than the parallel port because of the baud rate. The baud rate refers to the number of data transmitted per second, instead of byte (1 byte = 7bit + 1bit verification ), if such a serial port has a baud rate of bits/s, and a parallel port has a port of 80 bits/s, this indicates that the serial port transmits bits in one second, each with one packet, you can set the port to 80 bits per second for 10 requests, but the time required for 10 requests is 1 second. why is it slow? It is because the serial port implementation is simple, and the serial port under the same device can reach a higher theoretical transmission level.

 

Serial Interface
The serial port, or COM interface, is an extended interface using the serial communication protocol. The serial port appeared around 1980, and the data transmission rate was 115kbps ~ 230 kbps. The serial port is generally used to connect the mouse and external modem, as well as the old-fashioned camera and tablet devices. At present, some new boards have begun to cancel this interface.

 

Parallel Interface
The parallel interface, or LPT interface for short, is an extended interface using the parallel communication protocol. The data transmission rate of the parallel port is 8 times faster than that of the serial port. The data transmission rate of the standard parallel port is 1 Mbps, which is generally used to connect printers and scanners. Therefore, the parallel port is also called a print port.

In addition, both the serial port and the parallel port can achieve dual-host interconnection through direct cable connection, in which case data can only be transmitted at low speed. The functions and structure of the serial port and parallel port of the PC have not changed for many years. When using a serial port, in principle, each peripheral must be inserted in an interface. If all interfaces are used, you can only add a plug-in card to append interfaces. Strings and parallel ports are not only fast, but also inconvenient to use. For example, hot swapping is not supported. With the popularization of USB interfaces, it is rarely used at present, and with the popularization of BTX specifications, it will inevitably be eliminated.

The serial port and parallel port on the computer should be: hard disk, motherboard, and printer. The serial port is generally used to connect to some special external devices. For example, communication devices. The parallel port is usually used to connect printing devices. The serial port is relatively small, with a prominent needle exposed outside. The parallel port is generally larger than the serial port, usually red, with two rows of Holes

The serial port is described as a lane, and the parallel port has eight lanes.
8-bit (one byte) data can be transferred at the same time.
However, this is not because of mutual interference between eight-bit channels. The transmission speed is limited. In addition, when an error occurs during transmission, eight data records must be re-transmitted at the same time. There is no interference in the serial port. You can resend one character after an error occurs during transmission. So it is faster than the parallel port. Serial hard drives are so important.

The serial port and parallel port are different ports connected to peripherals. The two ports have different shapes, transmission speeds, and devices that can be connected.

Serial Transmission is one-to-one, like a string of beads.
The parallel port allows Concurrent Data Transmission of Multiple Digits at the same time.

Now there is a serial hard disk SATA interface, which is the same principle. The reason why it can be transmitted at a speed of 150 Mb/s is that it is thanks to its serial method, several Parallel signals cannot solve the interference between them very well at a relatively high frequency. Therefore, the parallel hard disk of ATA 13mbb/S has reached the limit and is replaced by stat. Another 80-channel ata100's parallel hard drive data cable, 40 of which are ground wires, is used to prevent interference between parallel signals.

Stat, the nominal bit/s speed, is actually the speed of 150 m/m
The fastest speed of a single hard disk is less than 100 Mb/s.
Generally, the speed is between 40-60 Mb/s,
Remember !!! Interface is not a bottleneck

 

Parallel pin function list
Pin function pin function
1 select the connection end, the low level is valid 10 OK, the low level is valid
2 Data tunnel 0 11 busy
3 Data Channel 1 12 paper shortage
4 Data Channel 2 13 select
5 Data tunnel 3 14 automatic, low-level valid
6 Data Channel 4 15 error, effective at low level
7 Data Channel 5 16 initialization, effective at low level
8 Data Channel 6 17 select input, low level valid
9 data channels 7 18 to 25 ground lines

 

List of 25-pin serial ports
Pin function pin function
1 null 11 null
2 send data 12 to 17 empty
3 receive data 18 Blank
4 send request 19 Blank
5. Send and clear 20. Data Terminal preparation is complete.
6. Data Preparation completed. 21 Blank
7 signal ground line 22 ring indicator
8 carrier detection: 23 to 24 null
9 blank 25 empty
10 Blank

 

9-pin serial port function list
Pin function pin function
1. Carrier Detection 6. Data preparation complete
2 send data 7 send requests
3 receive data 8 send clear
4. Data Terminal preparation completed 9. Ringing instructions
5. Signal ground