Computer hardware All interface detailed

CPU and external devices, memory connection and data exchange need to be implemented through the interface device, the former is called I/O interface, and the latter is called the memory interface. Memory usually in the CPU synchronization control work, the interface circuit is relatively simple, and I/O equipment a wide variety of the corresponding interface circuit is also different, so, it is customary to refer to the interface is just the I/O interface.

First, the concept of i/0 interface

1, the classification of the interface

I/O interface function is responsible for the implementation of the CPU through the system bus to the I/O circuit and peripheral devices together, according to the complexity of the circuit and equipment, I/O interface hardware is divided into two major categories:

(1) I/O interface chip

Most of these chips are integrated circuits, through the CPU input different commands and parameters, and control the relevant I/O circuit and simple peripherals for the corresponding operation, common interface chip such as timing/counter, interrupt Controller, DMA controller, parallel interface and so on.

(2) I/O interface control card

There are a number of integrated circuits in a certain logical group to become a component, or directly with the CPU on the motherboard, or a plug-in plug in the system bus slots.

They can be divided into serial interface, parallel interface, keyboard interface and disk interface according to the connection object of the interface.

2, the function of the interface

Because of the wide variety of computer peripherals, almost all of the use of electromechanical transmission equipment, so the CPU in the I/O device data exchange with the following problems:

Speed mismatch: I/O devices work much slower than the CPU, and because of the different kinds, the speed difference between them is also very large, such as hard disk transmission speed than the printer is much faster.

Timing mismatch: Each I/O device has its own timing control circuit, with its own speed transmission data, can not be unified with the CPU timing.

Information format mismatch: Different I/O devices Store and process information in different formats, for example, can be divided into serial and parallel, can also be divided into binary format, ACSII encoding and BCD encoding.

The type of information does not match: different I/O devices use different types of signals, some are digital signals, and some are analog signals, so the processing methods used are different.

For the above reasons, the data exchange between the CPU and the peripheral must be done through the interface, usually the interface has the following functions:

(1) Set up data storage, buffer logic to meet the CPU and peripheral speed difference between the interface is usually made up of some registers or RAM chips, if the chip is large enough can also achieve the transmission of bulk data;

(2) The ability to transform information formats, such as serial and parallel conversions;

(3) It can coordinate the difference of the type and level of information between CPU and peripheral, such as level conversion drive, number/die or module/number converter, etc.

(4) Coordination of timing differences;

(5) Address decoding and device selection function;

(6) Set interrupt and DMA control logic to ensure interrupt and DMA request signals are interrupted and DMA-enabled, and to complete the interrupt processing and DMA transfer after receiving the interrupt and DMA response.

3, the interface control mode

There are several ways in which the CPU controls peripherals through interfaces:

(1) Procedure Inquiry Way

This way, the CPU through I/O instructions to specify the current state of the peripherals, if the peripheral is ready, then the data input or output, otherwise the CPU waiting, circular query.

The advantage of this approach is that the structure is simple, only a small number of hardware circuit can be, the disadvantage is that the CPU speed is far higher than the peripheral, so usually in the waiting state, the efficiency is very low

(2) Interrupt handling mode

In this way, the CPU is no longer passively waiting, but can execute other programs, once the peripheral for data exchange ready, you can make a service request to the CPU, if the CPU should ring the request, it will temporarily stop the current program execution, to carry out the request corresponding to the service program, completed, Continue to execute the previously interrupted program.

The advantage of interrupt processing is obvious, it not only saves the CPU the time of querying peripheral state and waiting for peripherals to be ready, improves the working efficiency of CPU, but also satisfies the real-time requirement of peripherals. However, each I/O device needs to be assigned an interrupt request number and the corresponding interrupt service program, in addition to an interrupt controller (I/O interface chip) to manage the interrupt request from the I/O device, such as setting the interrupt mask, interrupt request priority, and so on.

In addition, the disadvantage of interrupt processing is that each transmission of a character to interrupt, start the interrupt controller, but also to retain and restore the site to continue the execution of the original program, the workload is very large, so if the need for a large number of data exchange, the performance of the system will be very low.

(3) DMA (Direct memory access) transfer mode

The most obvious characteristic of DMA is that it uses a special controller instead of the software to control the data exchange between the memory and the peripheral, without CPU intervention, which can greatly improve the efficiency of the CPU.

Before DMA data transfer, the DMA controller will request the bus control to the CPU, if the CPU allows, the control power will be surrendered, therefore, in the data exchange, the bus control power is mastered by the DMA controller, after the transmission is over, the DMA controller will return the bus control to the CPU.

Second, common interface

1. Parallel interface

At present, the parallel interface in the computer is mainly used as the printer port, the interface is no longer a 36-pin connector but a 25-pin D-connector. The so-called "parallel" refers to the 8-bit data transmission at the same time through parallel lines, so that the data transmission speed greatly increased, but the parallel transmission line length is limited, because the length of increase, interference will increase, error prone.

There are now five common types of intersections: 4-bit, 8-bit, half-8-bit, EPP and ECP, most PCs are equipped with 4-or 8-bit, many laptops with the INTEL386 chipset with EPP ports, and computers that support all IEEE1284-port specifications are equipped with ECP ports.

Standard parallel port 4-bit, 8-bit, half 8-bit: 4-bit mouth at a time can only enter 4-bit data, but output 8-bit data, 8-bit can be input and output at one time 8-bit data, half 8 bits can also.

EPP Port (enhanced parallel port): Developed by companies such as Intel, allowing 8-bit two-way data transfer to connect a variety of non-printer devices such as scanners, LAN adapters, disk drives, and CDROM drives.

ECP port (extended parallel port): Developed by Microsoft, HP, capable of supporting command cycles, data cycles, and multiple logical device addressing, DMA (direct memory access) can be used in a multitasking environment.

At present, almost all of the 586-machine motherboards are integrated parallel port sockets, labeled as Paralle1 or LPT1, is a 26-pin double row pin socket.

2, serial interface

Another standard interface for computers is the serial port, which now has at least two serial port COM1 and COM2. The serial port differs from the parallel port in that its data and control information is transmitted serially by one after another. In this way, although the speed is slower, but the transmission distance is longer than the parallel port, so long-distance communication should use a serial port. Typically, COM1 uses a 9-pin D-shaped connector, while COM2 some use an old-fashioned DB25 pin connector. Electric + brain * d + repair-know-net (w_ww*dnw_xzs*co_m)

3. Disk interface

(1) IDE interface

The IDE interface, also called the ATA port, can only receive two hard drives with a capacity of no more than 528M, and the cost of the interface is very low, so it is very popular during the 386 and 486 periods. However, most IDE interfaces do not support DMA data transfer, and only standard PCI/O port directives are used to transfer all commands, states, and data. Almost all 586 motherboards are integrated with two 40-pin dual-row PIN IDE socket sockets, labeled IDE1 and IDE2 respectively. Electric + brain * d + repair-know-net (w_ww*dnw_xzs*co_m)

(2) Eide interface

The Eide interface is much better than the IDE interface and is currently the most popular interface. First, the peripherals it supports are no longer 2 but 4, supported devices in addition to the hard disk, including CD-ROM drive disk backup devices, and so on. Second, the Eide standard cancels the 528MB limit and replaces it with the 8GP limit. Third, the Eide has a higher data transfer rate and supports PIO Mode 3 and Mode 4 standards.

4, SCSI interface

scsi (SMALLCOMPUTERSYSTEMINTERFACE) Small computer system interface, which is widely used as a SCSI interface in computer graphics processing and network services. In addition to hard drives, SCSI interfaces can also connect CD-ROM drives, scanners, and printers, which have the following characteristics:

7 Peripherals can be connected at the same time;

The bus is configured to parallel 8-bit, 16-bit, or 32-bit;

Allow maximum hard disk space of 8.4GB (some of which have reached 9.09GB);

Higher data transfer rate, IDE 2MB per second, SCSI can usually reach 5MB per second, FASTSCSI (SCSI-2) can reach 10MB per second, the latest SCSI-3 can even reach 40MB per second, and Eide up to 16.6MB per second;

The cost is much higher than the IDE and Eide interfaces, and the SCSI interface hard disk must be used in conjunction with the SCSI interface card, and the SCSI interface card is much more expensive than the IED and Eide interfaces.

SCSI interfaces are intelligent and can communicate with each other without increasing the burden on the CPU. When transferring data between the IDE and the Eide device, the CPU must intervene, and the SCSI device is active in the data transfer process and can be executed within the SCSI bus until the CPU is completed.

5, USB interface

The latest USB serial interface standard is launched by a large company, such as Microsoft, Intel, Compaq, IBM, which provides a hot plug and Play connection outside the chassis, the user does not have to open the chassis, power off when connecting the peripherals, but uses "the Cascade" way, Each USB device is connected to a USB socket on a peripheral with a USB plug that itself provides a USB socket for the next USB device, in which case a USB controller can connect up to 127 peripherals, and the distance between each peripheral can reach 5 meters. USB Unified 4-pin round plug will replace many of the chassis after the string/mouth (mouse, MODEM) keyboard and other plugs. 　　USB can intelligently identify the insertion or disassembly of peripheral devices on the USB chain. In addition to being able to connect keyboards and mice, USB can also connect to low speed peripherals such as ISDN, telephone systems, digital stereos, printers, and scanners.

Third, I/O expansion slot

I/O expansion slot is the path of I/O signal transmission, is the extension of the system bus, can insert any standard options, such as display card, decompression card, modem card and sound card. With I/O expansion slots, the CPU is able to read and write to all I/O interface chips and control cards that are connected to the channel.

Depending on the type of bus, the expansion slots on the motherboard can be divided into Isa, EISA, MAC, VESA, and PCI.

(1) ISA slots

Black, divided into 8-bit, 16-bit two kinds. The 16-bit expansion slots can be plugged into 8-bit and 16-bit control cards, but 8-bit expansion slots can only be inserted into 8-bit cards.

(2) EISA Slots

Brown, shape, length is the same as 16-bit ISA card, but the depth is large, you can insert the ISA and EISA control card.

(3) VESA Slots

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Brown, located below the 16-bit ISA expansion slot and used with the ISA slot.

(4) PCI Slots

White, as long as the VESA slot, parallel to the ISA slot, does not need to be used in conjunction with the ISA slot, and can only be plugged into the PCI control card. PCI slots occupy the location of the ISA slot due to limited space on the motherboard