io接口的作用（The function of IO interface）
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The function of I/O interface
Host and external exchange information is called input / output (I/O). The information exchange between the host and the outside is carried out through the input / output device. General input / output devices are the product of mechanical or electromechanical combination, such as conventional peripheral keyboard, display, printer, scanner, disk, mou, with respect to the central processor speed is much slower. In addition, the signal format and data format of different peripherals are also different. Therefore, the external equipment can not be directly connected with the CPU, the corresponding circuit to complete the speed matching between them, signal conversion, and complete some control functions. Usually a buffer circuit between the host and the peripheral device is called the I/O interface circuit, referred to as the I/O interface (Interface), as shown in figure 7.1. For the host, the I/O interface provides working status and data of external devices; for external devices, I/O memory interface all the commands and data to the host peripherals, so that the coordination between the host and peripherals.
自我分析For micro computer, the design of CPU microprocessor, is not part of design interface between it and peripherals, but the input / output interface circuit design of equipment into relatively independent parts,
through the micro computer hardware peripherals and they will all types of CPU connected together to form a complete. Therefore, a microcomputer input / output system should include the I/O interface, the I/O device and the related control software. The comprehensive processing
ability, system reliability, compatibility, performance and price ratio of a microcomputer system and even the u of an occasion are cloly related to the I/O system. The input / output system is an important part of the computer system, any high performance computer, if there is no high quality input / output system matched with the work of high performance computers cannot play out.
Information exchanged between 7.1.2 CPU and peripherals
The information exchanged between the host and the I/O device can be divided into three categories: data information, state information and control information.石碣中学
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I. data information
公司法修改Data information can be divided into three forms: digital quantity, analog quantity and switching quantity.
1. digital quantity
Digital quantity is the data that the computer can nd, receive and process directly. For example, the information exchanged by I/O peripherals such as keyboards, monitors, printers, and disks, etc., is exchanged with CPU. They are binary numbers or symbols reprented by ASCII codes.
2. analog
When the computer is applied to the control system, the physical input information is continuously changing from the scene, such
as temperature, pressure, flow, displacement, humidity, the physical quantity through the nsor and amplified by analog voltage or current, the analog quantity required to go through the conversion of the analog to digital. (A / D) to enter the computer. In turn, the computer output control signal is digital quantity, also must first through the digital analog to analog conversion (D / A conversion), the digital quantity into analog to control the scene.
3. switch quantity
吃西瓜大比拼The switch amount can indicate two states, such as the disconnection and closing of the switch, the operation and stop of the machine, the opening and closing of the valve, etc.. The switches usuall
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y have to pass the corresponding level conversion to connect with the computer. The amount of switch can be expresd only by one bit and two numbers.
Two. Status information
State information, as the contact information between CPU and peripheral data, reflects the working state of the current peripherals, and is nt to the CPU through the interface through the peripherals. By reading the state signal, the CPU can know whether the data of the input device is ready and the output device is idle. The input device, usually ready (READY) signal level to the input data is ready; for the output device, is busy (BUSY) signal level of said output equipment is in idle state, such as idle, can receive CPU output information,
Otherwi, CPU will pau the number. Therefore, the state
information can guarantee the correct data exchange between CPU and peripherals.
Three. Control information
The control information is transmitted by CPU to the peripheral through the interface, and CPU nds the control information to t up the working mode of the peripheral (including the interface) a
nd controls the work of the peripheral. Such as peripheral start signal and stop signal is the common control information. In fact, the control information is often different with the specific working principle of the peripheral.
Although the data information and the state information and control information meaning is different, but in the micro computer system, CPU exchange information through the interface and peripherals, can only u the input and output instructions (IN) (OUT) to transmit data, so the state information and control information are transmitted as data, namely state information as a kind of input data, and control information as an output data, so the state information and control information through the data bus to transfer. But in the interface, the three kinds of information are stored in different registers.
美术鉴赏The basic structure of 7.1.3 I/O interface
The basic structure of the I/O interface is shown in figure 7.2. Each interface circuit contains a t of registers, when CPU and peripherals exchange information, all kinds of information
in the interface into different registers, commonly referred to as the registers I/O port, referred to as Port (port). Ud to transfer data between CPU and peripherals (such as digital prervation, and
specific character encoding, etc.) on the input / output data from the buffer data register called the data port to the status register; storage peripherals or interface component itlf state called port state; ud to store the CPU nt to the command register to control peripherals the call control port.
Just as every memory cell has a physical address, each port also has an address corresponding to the port address. With port address, the input / output operation of CPU to the peripherals is actually the read / write operation of the ports in the I/O interface. The data port is generally bidirectional. Whether the data is input or output depends on the read / write control signal nt by the CPU to the interface circuit when the port address is operated. The state port only for input operation, the control port only for output operation, so, sometimes in order to save the system address space in the design interface of the two ports often share a port address and the read / write signal to choo access.
It should be pointed out that the address ud for the input / output operation is always for the port, not for the interface. Interfaces and ports are two different concepts, and veral ports with the corresponding control circuit constitute the interface.
Addressing of 7.1.4 I/O ports
