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Questions and Answers
What is the duration of each clock cycle if the CPU is operating at 8 MHz?
What is the duration of each clock cycle if the CPU is operating at 8 MHz?
What is the total duration of a normal bus cycle?
What is the total duration of a normal bus cycle?
What is the purpose of the wait state in a bus cycle?
What is the purpose of the wait state in a bus cycle?
How many clock cycles does the CPU maintain the address on the address bus during a READ cycle?
How many clock cycles does the CPU maintain the address on the address bus during a READ cycle?
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What is the instruction that reads data from the input port at address 0FEH?
What is the instruction that reads data from the input port at address 0FEH?
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What is the state of the bus when no bus cycles are required?
What is the state of the bus when no bus cycles are required?
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What is the purpose of the ALE signal in the 8086 memory read bus cycle?
What is the purpose of the ALE signal in the 8086 memory read bus cycle?
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In which T-state does the CPU enable the RD signal in the 8086 memory read bus cycle?
In which T-state does the CPU enable the RD signal in the 8086 memory read bus cycle?
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What is the purpose of the WR signal in the 8086 memory write bus cycle?
What is the purpose of the WR signal in the 8086 memory write bus cycle?
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What is the difference between isolated I/O and memory-mapped I/O?
What is the difference between isolated I/O and memory-mapped I/O?
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What is the purpose of I/O ports?
What is the purpose of I/O ports?
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How many types of I/O interfaces are mentioned in the text?
How many types of I/O interfaces are mentioned in the text?
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What is the size of the I/O address space?
What is the size of the I/O address space?
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What is the maximum port address for an 8-bit port?
What is the maximum port address for an 8-bit port?
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How are I/O devices treated in memory-mapped I/O?
How are I/O devices treated in memory-mapped I/O?
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What instruction is used to access memory-mapped I/O devices?
What instruction is used to access memory-mapped I/O devices?
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What is the range of addresses assigned for I/O devices in memory-mapped I/O?
What is the range of addresses assigned for I/O devices in memory-mapped I/O?
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What is the main difference between isolated I/O and memory-mapped I/O?
What is the main difference between isolated I/O and memory-mapped I/O?
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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.