Intel微机原理第11章(基本I／O接口)-1.ppt

第11章 基本I/O接口 基本I/O（输入/输出）接口简介 独立编址I/O与存储器映像I/O 接口信号交换 接口电路 I/O端口译码 可编程外设接口电路(82C55) 可编程键盘/显示器接口芯片8279 可编程时间间隔定时器8254 可编程通信接口芯片16550 数/模转换器和模/数转换器 11-1 Introduction to I/O interface 11-1-1 接口功能 计算机两部件之间的界面称之为接口。 接口的主要功能是： （1）数据缓冲及输入、输出 （2）寻址功能 （3）命令译码 （4）同步、联络和控制功能 11-1-2 Basic I/O Instructions We discussed IN, OUT, INS and OUTS as instructions for the transfer of data to and from an I/O device. (see p384 table 11-1) IN and OUT transfer data between an I/O device and the microprocessor’s accumulator (AL, AX or EAX). The I/O address is stored in: Register DX as a 16-bit I/O address (variable addressing). The byte, p8, immediately following the opcode (fixed address). IN AL, 19H ;8-bits are saved ;to AL from I/O port 19H. IN EAX, DX ;32-bits are saved to EAX. OUT DX, EAX ;32-bits are written ;to port DX from EAX. OUT 19H, AX ;16-bits are written ;to I/O port 0019H. Notice: Only 16-bits (A0 to A15) are decoded. Address connections above A15 are undefined for I/O instructions. 0000H-03XXH are used for the ISA bus. INS and OUTS transfer to I/O devices (which address is in DX) using ES:DI and DS:SI, respectively. 11-1-3 Isolated versus Memory-Mapped I/O独立编址I/O与存储器映像I/O Isolated and Memory-Mapped I/O: In the Isolated scheme, IN, OUT, INS and OUTS are required. In the Memory-mapped scheme, any instruction that references memory can be used. Isolated versus Memory-Mapped I/O Isolated I/O 8-bit port addresses used to access system board device, e.g. timer and keyboard. 16-bit port addresses used to access serial and parallel ports, hard drivers, etc. PC I/O Address Map 11-1-4 Basic I/O Interface The basic input device (to the microprocessor) is a set of tri-state buffers. The basic output device (from the microprocessor) is a set of latches. Basic I/O Interface Basic I/O Interface 11-1-5 Handshaking 握手信号 I/O devices are typically slowe