What is not a serial interface in a microcomputer?

What does not belong to the serial interface is "LPT". The LPT interface belongs to the category of parallel port and is generally used to connect printers or scanners. It is an enhanced bidirectional parallel transmission interface. Each bit of data in the parallel interface is transmitted in parallel, and it is usually transmitted in units of bytes (8 bits) or bytes (16 bits); the parallel interface means that all bits of data are transmitted at the same time, and its characteristic is the transmission speed. Fast, but when the transmission distance is long and the number of bits is large, the communication lines will be complicated and the cost will increase.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

In microcomputers, what is not a serial interface is "LPT".

Among the interfaces equipped with daily microcomputers, COM1, PS/2, VGA, RJ-45, and USB interfaces all support serial For communication, only the LPT interface belongs to the category of parallel port, and it is rarely used.

LPT (line print terminal, print terminal) is used to use printers or other devices. It is an enhanced two-way parallel transmission interface. Before the USB interface appeared, it was the most commonly used interface for scanners and printers. The device is easy to install and use, but is slow.

LPT interface (parallel port): generally used to connect printers or scanners. Its default interrupt number is IRQ7, using a 25-pin DB-25 connector.

There are three main working modes of the parallel port:

• SPP standard working mode. SPP data is simplex and one-way transmission, with a slow transmission rate of only 15Kbps. However, it is widely used and is generally set as the default working mode.

• EPP enhanced working mode. EPP uses bidirectional half-duplex data transmission, and its transmission rate is much higher than SPP, up to 2Mbps. Many peripherals already use this working mode.

• ECP extended working mode. ECP uses bidirectional full-duplex data transmission, and the transmission rate is higher than EPP, but it supports fewer devices.

Communication principle of parallel interface

In the parallel interface, all data are transmitted in parallel, which is usually in bytes (8 bits) Or byte (16 bits) for data transmission.

As shown in the figure below, the parallel interface in the figure is a dual-channel interface that can complete data input and output. Among them, the input/output of data is realized by the input/output buffer, the status register provides status information for CPU query, and the control register receives various control commands from the CPU.

#During the data input process: the input device sends data to the interface and makes "data input ready" valid. When the interface sends data to the input buffer register, the "data input reply" signal is valid. When the peripheral receives the reply signal, it cancels the "data input ready" and data signals. At the same time, the corresponding bit in the status register ("data input ready") is valid for CPU query. Of course, the interrupt method can also be used to issue an interrupt request to the CPU. After the CPU reads the data, the interface will automatically reset the "data input ready" bit in the status register. Then, the CPU enters the next input process.

During the data output process: when the data output by the CPU is sent to the data output buffer register, the interface will automatically clear the "output ready" status bit in the status register, and send the data to the output device, output After the device receives the data, it sends a response signal to the interface to tell the interface that the data has been received. After the interface receives the signal, it sets the "output ready" status bit in the status register to "1". Then, the CPU enters the next output process.

The main features of parallel interface

The parallel interface means that all bits of data are transmitted at the same time. It is characterized by fast transmission speed, but when the transmission distance is long and the number of bits is If it is too long, the communication lines will become complicated and the cost will increase.

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