8086 Microprocessor I/O Interfacing Quiz and Flashcards: Memory and I/O

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Questions and Answers

What is the duration of each clock cycle if the CPU is operating at 8 MHz?

250 ns

200 ns

125 ns (correct)

500 ns

What is the total duration of a normal bus cycle?

400 ns

1000 ns

600 ns

500 ns (correct)

What is the purpose of the wait state in a bus cycle?

To speed up the bus cycle

To produce the data

To decode the address

To wait for very slow devices (correct)

How many clock cycles does the CPU maintain the address on the address bus during a READ cycle?

1 clock cycle Signup and view all the answers

What is the instruction that reads data from the input port at address 0FEH?

IN AL, 0FEH Signup and view all the answers

What is the state of the bus when no bus cycles are required?

Idle state Signup and view all the answers

What is the purpose of the ALE signal in the 8086 memory read bus cycle?

To place the address on the Address Bus Signup and view all the answers

In which T-state does the CPU enable the RD signal in the 8086 memory read bus cycle?

T2 Signup and view all the answers

What is the purpose of the WR signal in the 8086 memory write bus cycle?

To write data to memory Signup and view all the answers

What is the difference between isolated I/O and memory-mapped I/O?

Isolated I/O uses separate address space Signup and view all the answers

What is the purpose of I/O ports?

To identify I/O devices Signup and view all the answers

How many types of I/O interfaces are mentioned in the text?

Two Signup and view all the answers

What is the size of the I/O address space?

64Kbytes Signup and view all the answers

What is the maximum port address for an 8-bit port?

00FFH Signup and view all the answers

How are I/O devices treated in memory-mapped I/O?

As memory locations Signup and view all the answers

What instruction is used to access memory-mapped I/O devices?

Memory Read/Write instruction Signup and view all the answers

What is the range of addresses assigned for I/O devices in memory-mapped I/O?

E0000H to E0FFFH Signup and view all the answers

What is the main difference between isolated I/O and memory-mapped I/O?

Instruction type Signup and view all the answers

Study Notes

I/O Examples

Direct I/O example: IN AL, 0FEH - data is transferred in one cycle
Variable I/O example: MOV DX, 0A00H; MOV AL, DX; BL, AL - address of I/O port is specified

Bus Cycle Timing

Each bus cycle consists of 4 clock cycles (4 T-States)
If the CPU operates at 8 MHz, each clock cycle is 125 ns long
Length of a normal bus cycle is 4 x 125 ns = 500 ns
External devices connected to the microprocessor have the following timing requirements for a READ cycle:
- CPU produces the address on the address bus and maintains it for 1 clock cycle
- External device has 1 clock cycle to decode and locate the location
- External device produces the data and maintains it on the data bus for 2 clock cycles

Bus Cycle States

Idle state: no bus cycles are required, and the bus remains idle
Wait state: states inserted between T3 and T4 of the current bus cycle, used to wait for slow devices

8086 Memory Read Bus Cycle

T1: CPU places address on the address bus and sets ALE to 1
T2: CPU enables the RD signal
T3: CPU sets ALE to 0, and memory puts data on the data bus
T4: CPU completes read from memory

8086 Memory Write Bus Cycle

T1: CPU places address on the address bus and sets ALE to 1
T2: CPU enables the WR signal and places data on the data bus
T3: CPU maintains the data on the data bus
T4: CPU completes write to memory

Types of Input/Output Interface

I/O ports: used to identify which device we are communicating with
Two methods of identifying ports:
- Isolated I/O
- Memory-mapped I/O

Isolated Input/Output

8088/8086 support separate I/O and memory address spaces
I/O devices are treated separately from memory
Special instructions are used to read and write from I/O devices
I/O address space is 64K bytes
Ports can have an address of 8 bits or 16 bits

Memory-Mapped I/O

I/O devices are placed within the memory address space of the processor
Some of the memory space is dedicated to I/O devices
Reading from and writing to memory-mapped I/O devices uses the same instructions as reading from and writing to memory locations

Isolated vs. Memory-Mapped I/O

Isolated I/O: uses special I/O instructions
Memory-mapped I/O: uses memory read/write instructions

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Description

Test your understanding of the 8086 microprocessor's memory and I/O interfacing, including memory read and write bus cycles. Learn about the CPU's interaction with the address bus, data bus, and control signals. Assess your knowledge of processors and assembly language.