An interface is a connection device that links the CPU with peripheral devices, used to buffer and forward data between them. It plays a crucial role in ensuring smooth communication and efficient operation between the high-speed CPU and slower peripherals.
Why do we need an interface?
(1) **Solving Timing Coordination and Communication Problems**
The CPU operates at high speeds, such as the 8086-1 with a clock frequency of 10MHz, where one clock cycle takes just 100ns, and the basic bus cycle is 400ns. In contrast, peripherals like teletypewriters or industrial sensors may operate on millisecond or second-scale intervals. To ensure the CPU can work efficiently while adapting to different peripheral speeds, an I/O interface is essential. This interface includes components like data latches, buffers, status registers, and interrupt control circuits, enabling asynchronous communication and improving CPU utilization.
(2) **Data Format Conversion and Matching**
The CPU typically processes parallel data, but many peripherals use serial data for transmission (e.g., long-distance communication or pulse signals from encoders). The interface converts between these formats, allowing the CPU to receive and send data in compatible forms. This conversion is usually handled by specific interface chips under CPU control.
(3) **Managing CPU Load and Port Selection**
Directly connecting multiple peripherals to the CPU’s data and address buses would overload the system. The interface helps distribute the load, prevents signal conflicts, and allows selective access to peripheral ports. By using tri-state gates and control signals, only the selected peripheral communicates with the CPU at any given time, making the system more reliable and scalable.
In addition, interfaces often support programmable functions and error detection. For example, a port can be configured as input or output via software, and many serial interface chips include parity checks or redundancy verification.
What parts make up an interface hardware?
(1) **Basic Logic Circuits**
Includes command registers, status registers, and data buffer registers.
(2) **Port Address Decoding Circuit**
Determines which register (port) is selected based on the address bus.
(3) **Optional Circuits**
May include connections to an interrupt controller or other components for advanced operations.
What is the function of interface software?
A complete device driver program typically includes initialization, transfer setup, master control, termination, and user interface blocks. These programs act as standardized software interfaces, enabling communication between the CPU and peripherals.
What are the forms of interface circuits?
- **Fixed Structure:** SSI, MSI ICs
- **Semi-Fixed Structure:** GAL, PAL
- **Programmable Structure:** Programmable chips
- **Intelligent Structure:** Includes microprocessors
How does the CPU exchange data with the interface?
- **Polling Mode:** The CPU checks if the peripheral is ready before transferring.
- **Interrupt Mode:** The peripheral sends an interrupt request when it's ready, and the CPU handles it.
- **DMA Mode:** Direct Memory Access allows data transfer without CPU intervention, improving performance.
What is an I/O port?
I/O ports are registers in the interface circuit that store data, status, and control information. They allow the CPU to directly read from or write to them. Common types include:
- **Data Port:** Stores data for exchange between the host and peripheral.
- **Status Port:** Indicates the current state of the peripheral (e.g., Ready, Busy).
- **Command Port:** Holds commands sent from the CPU to control the peripheral.
I/O Port Addressing Modes
- **Memory-Mapped I/O:** Treats I/O ports as memory locations, accessible via standard memory instructions.
- **I/O Instruction Mode:** Uses special IN/OUT instructions to access separate I/O address spaces, commonly found in systems like the 8086.
I/O Instructions (Intel 8086)
Examples:
- `IN AL, PORT8` – Read from an 8-bit port into AL.
- `OUT DX, AL` – Write AL to the port addressed by DX.
How to decode I/O port addresses?
The port chip's selection signal (CS) is generated by the address and control buses. Designing the decoding circuit ensures the CPU accesses the correct port during I/O instructions.
Types of I/O Port Address Decoding Circuits:
- **Fixed Single Port Decoding:** Uses gate circuits or decoders; the address cannot be changed after design.
- **Optional Decoding:** Allows changing the port address using DIP switches.
- **Programmable Logic Arrays:** Offers flexible decoding through programmable logic.
Interface Input/Output Methods:
(1) **Unconditional Transmission**
Used for simple peripherals that are always ready, like LED displays.
(2) **Polling Method**
The CPU continuously checks the interface status until it's ready.
(3) **Interrupt Method**
The peripheral requests an interrupt when it's ready, allowing the CPU to respond.
(4) **DMA Method**
For large data transfers, the DMA controller takes over the bus, allowing direct memory-to-peripheral transfers without CPU involvement.
DMA Process Example:
When a disk needs to transfer data, the CPU initializes the DMA controller, which then takes control of the bus. After receiving a DMA request, the controller transfers data directly between the disk and memory, freeing the CPU for other tasks. Once done, the controller releases the bus back to the CPU.
At present, flat Zinc bar is the ideal material for the zinc static and dynamic balance block of vehicle wheel, with good corrosion resistance.
Excellent mechanical properties,elongation is up to 20% or more,the yield of balance pieces stamping is high.
Product specification: Ñ„19mm(width)*2.65mm(thick)
Product packing: 30-150kgs(special packaging specifications can be negotiated)
Flat Zinc Bar,Anode Zinc Bar,Galvanized Zinc Flat Bar,Zinc Coated Steel Flat Bar
Shaoxing Tianlong Tin Materials Co.,Ltd. , https://www.tianlongspray.com