A brief overview of computer interface Technology

Due to the mismatch of speed, data format mismatch, information type mismatch, in order to solve the problem of information exchange between peripheral and host, it is necessary to reference an intermediary-interface of information exchange. Common computer interfaces are parallel interfaces, serial interfaces, and disk interfaces. Parallel interface: Data presentation in parallel interface is a parallel transmission, usually a byte (8 bits) or a word (16 bits), parallel interface includes the host bus directly connected to the input/output data buffer and a set of data lines, including the contact signal, data transmission efficiency is high, but the effective distance is short, The more typical representative is the printer. Serial interface: transmission mode serial, data is a bit transmitting place. Serial interface with strong anti-jamming capability, suitable for long-distance transmission, PC host has two serial interface COM1 and COM2. The disk interface includes the IDE interface and the Eide interface. The Eide interface is currently the most popular interface, peripheral equipment supports hard disk, CD-ROM drive, disk backup device. scsi (Small computer system Interface) interface is a small computer system interface, is widely used as a hard disk interface and CD-ROM drives, scanners and other devices, SCSI interface is intelligent, the device can communicate with each other without increasing the burden of the CPU, While transferring data between the IDE and the Eide device, the CPU must intervene, but the SCSI cost is too high. USB interface in the current PC field, the USB interface provides plug-and-play connection outside the chassis, the USB bus is "cascaded" mode, each USB device with a USB plug connected to a peripheral USB socket, and from itself has provided a USB plug to the next USB device to use, With this cascade, a USB controller can connect up to 127 peripherals.

Host through the interface external control methods are:

1. Query method: The host through the I/O instruction loop to access the status of the current peripheral, if the peripheral is ready, the data transfer, otherwise the host will continue to query. Pros: Simple to implement. Disadvantage: Because the host speed is relatively slow, so the host is often in a waiting state, the efficiency is greatly reduced.

2. Interrupt mode: The host does not cycle through the peripherals, but does other work. The peripheral will check the status of its own, once the data can be transferred, immediately send a signal to the host to make data transfer requests. If the host responds to this request, it pauses the current work and transmits the data to the peripheral, and then resumes the original work after completion. Interruption can significantly improve the efficiency of the host. The disadvantage is that each data transmission needs to go through the start interrupt Controller, save the field data, restore the field data process, which will consume a lot of host resources.

3.DMA mode: DMA (direct memory access) means direct storage access, and one of the most obvious features of this approach is the use of a special hardware circuit--DMA controller to achieve data transfer between memory and peripherals. Before the DMA transfer, the DMA controller will request control of the data bus to the host and surrender control if the host allows it. Therefore, when the DMA mode for data transmission, the bus control is controlled by the DMA controller, after the completion of data transmission, the DMA controller will return the bus control to the host.

The DMA controller or interface typically consists of four registers:

Status control registers, data registers, address registers, and byte counters.

These registers need to be initialized before the information is sent. That is, in the input and output program, the individual registers are written to the initialization control Word using assembly language instructions.

A brief overview of computer interface Technology