信息技术.小型计算机系统接口(SCSI).第112部分:平行接口-3(SPI-3

[中文适用范围]： SCSI 协议旨在提供高效的点对点 I/O 总线，其最大主机和外设数量由总线宽度（8 或 16）决定。 数据可以异步或同步传输，传输速率主要取决于设备实现和电缆长度。 SCSI 是一种 I/O 接口，可以在多种介质和传输速率下运行。 SCSI 中并行接口的目标是： a) 为主机提供一类设备中的设备独立性。 因此，不同的磁盘驱动器、磁带驱动器、打印机、光学介质驱动器和其他SCSI设备可以添加到主机，而不需要修改通用系统硬件； b) 提供兼容性，以便在系统工程正确完成的情况下，符合标准的 SCSI-2 和 SPI-2 设备可以与 SPI-3 设备互操作。 符合标准的 SCSI-2 和 SPI-2 设备应以可接受的方式响应以拒绝 SPI-3 协议扩展。 SPI-3 协议扩展被设计为允许此类拒绝，从而允许 SCSI-2 和 SPI-2 设备继续操作而无需使用扩展。 该国际标准增强了 SPI-2 标准的功能，旨在成为超越 SPI-2 标准的新设计的选择。 一些新功能包括：fast-80 数据传输、双转换 (DT) 传输和并行传输上的 CRC。 [外文原描述]： The SCSI protocol is designed to provide an efficient peer-to-peer I/O bus with the maximum number of hosts and peripherals determined by the bus width (8 or 16). Data may be transferred asynchronously or synchronously at rates that depend primarily on device implementation and cable length. SCSI is an I/O interface that may be operated over a wide range of media and transfer rates. The objectives of the parallel interface in SCSI are: a) To provide host computers with device independence within a class of devices. Thus, different disk drives, tape drives, printers, optical media drives and other SCSI devices may be added to the host computers without requiring modifications to generic system hardware. b) To provide compatibility such that conforming SCSI-2 and SPI-2 devices may interoperate with SPI-3 devices given that the systems engineering is correctly done. Conforming SCSI-2 and SPI-2 devices should respond in an acceptable manner to reject SPI-3 protocol extensions. SPI-3 protocol extensions are designed to be permissive of such rejections and thus allow SCSI-2 and SPI-2 devices to continue operation without requiring the use of the extensions. This international standard enhances the functionality of the SPI-2 standard, and is intended to be the choice for new designs over the SPI-2 standard. Some new features are: fast-80 data transfers, double transition (DT) transfers, and CRC on parallel transfers.