微机原理与接口技术第七章作业详解.doc

Chapter 7 3.(1) Program-controlled I/O: All control is directly under the control of the program, so changes can be readily implemented. The order in which devices are serviced is determined by the program, this order is not necessarily fixed but can be altered by the program, as necessary. It is relatively easy to add or delete devices. But a great deal of time may be spent on testing the status inputs of the I/O devices, when the devices do not need servicing. (2) Interrupt-controlled I/O: It is accomplished by having the I/O device generate an interrupt signal which is tested directly by the hardware of the CPU. The simplest type of interrupt facility is that the processor executes a subprogram branch at some specific address whenever an interrupt input is detected by the CPU. The return address is saved by the processor as a part of the interrupt process. (3) DMA: Direct memory access (DMA) is a feature of modern computers which allows certain hardware subsystems within the computer to access system memory independently of the central processing unit (CPU). In the process of data transmitting, the DMA controller is participated in the process, and don’t need the interference of the CPU. 6. MOV DX ,43H MOV AL OUT DX,AL 7. Suppose the address of 8255 is 0FFE0H~0FFE3H. The program is as follows: DATA SEGMENT DB 100H DUP（？） DATA ENDS CODE SEGMENT ASSUME CS：CODE ，DS DATA START：MOV AX,DATA MOV DS,AX MOV AL MOV DX,0FFE3H OUT DX,AL MOV DX, 0FFE0H IN AL,DX INC DX NOT AL OUT DX,AL RET CODE ENDS END START Suppose the port address of 8254 is 40H-43H, the control word of counter 0 is =30H, and the count constant is 1000. The initialization program is as follows: MOV AL,30H OUT 43H,AL MOV AX,1000 OUT 40H,AL MOV AL,AH OUT 40H,AL The port address of 8254 is 38H-3BH. The control word of counter 0 is=36H. The count constant is 100K*10ms=1000. The init