I/O System Design 1. Show two ways of reading input port 40H. What instructions
ID: 3691845 • Letter: I
Question
I/O System Design
1. Show two ways of reading input port 40H. What instructions are required?
2. Explain the processor bus activity when OUT20, AL executes. Assume a minmode system.
3. Design a minmode full port address decoder for input/output port B0. You must generate active-low RDB0 and WRB0 signals.
4. Design a minmode full port address decoder for input ports B0 through B7. Eight individual port select outputs should be generated.
5. What changes must be made to the designs of Questions 3 and 4 for a maxmode system?
6. Design a minmode partial-address decoder for an output port whose binary address is 10x01x1x11111111, where X is a don’t care bit. What are all possible port address ranges for this decoder?
Explanation / Answer
1.
•One type of instruction transfers information
to an I/O device (OUT).
•Another reads from an I/O device (IN).
•Instructions are also provided to transfer strings of data between memory and I/O.
–INS and OUTS, found except the 8086/8088
2.
processor bus activity when OUT20 introduced, AL will execute, and minmode system is explained below.
The three buses of the 8086 and 8088 address bus ,data micro control fuction exactly the same way as those of any other microprocessor .if data are written to the memory , the microprocessor outputs the memory address on the addressbus,oututs the data to be written into memory on the data bus , and issue a write ( WR) to memory and =0
The 8086 and =1 for the 8088 .
4.
–Maximum mode
•S2, S1, S0 connect directly to 8288
0 0 0 INTA Interrupt Acknowledgment
0 0 1 IORC Read I/O Port
0 1 0 IOWC Write I/O Port
0 1 1 NONE Halt
1 0 0 MRDC Code Access
1 0 1 MRDC Read Memory
1 1 0 MWTC Write Memory
1 1 1 Passive None