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Questions and Answers
During a memory write cycle, what is the purpose of the ALE pin?
During a memory write cycle, what is the purpose of the ALE pin?
Which bus is responsible for fetching data from the CPU during a memory write cycle?
Which bus is responsible for fetching data from the CPU during a memory write cycle?
In a memory write cycle, when is the RD¯ signal expected to be?
In a memory write cycle, when is the RD¯ signal expected to be?
What is the significance of S0 and S1 being set to 1 and 0 respectively during a memory write cycle?
What is the significance of S0 and S1 being set to 1 and 0 respectively during a memory write cycle?
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Which type of interrupt requires the processor to execute an interrupt service routine (ISR)?
Which type of interrupt requires the processor to execute an interrupt service routine (ISR)?
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When an interrupt occurs, what does the processor typically do?
When an interrupt occurs, what does the processor typically do?
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What type of signal is an interrupt in computer architecture?
What type of signal is an interrupt in computer architecture?
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'ISR' in computer architecture stands for:
'ISR' in computer architecture stands for:
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Study Notes
Control Signals
- Control signals convey both command and timing information between system modules.
- Timing signals confirm the validity of data and address information.
- Command signals dictate the specific operations to be executed.
Typical Control Lines
- Memory Write: Initiates the writing of data from the bus to the addressed location.
- Memory Read: Transfers data from the addressed location to the bus.
- I/O Write: Outputs data from the bus to the specified I/O port.
- I/O Read: Transfers data from the addressed I/O port to the bus.
Control Bus Signals
- Transfer ACK: Confirms reception or placement of data on the bus.
- Bus Request: Indicates a module's need to acquire bus control.
- Bus Grant: Confirms that a requesting module has been granted bus control.
- Interrupt Request: Signals that an interrupt is pending.
- Interrupt ACK: Acknowledges recognition of the pending interrupt.
- Clock: Synchronizes operations across modules.
- Reset: Initializes all system modules for operation.
Bus Operation
- To send data, a module must obtain bus control and then transfer data via the bus.
- To request data from another module, a module must also gain bus control and send a request over the control and address lines, then wait for data to be returned.
OMMII
- Facilitates fetching one byte from an I/O port, requiring three T-States.
- Enables writing one byte to an I/O device, also requiring three T-States.
Opcode Fetch Cycle
- The opcode fetch cycle requires four T-States, labeled T1 to T4.
- The ALE pin is activated during the first T-State.
- Data lines AD0-AD7 fetch the opcode and store the lower byte of the Program Counter; A8-A15 store the higher byte.
- IO/M¯ is low, indicating a memory operation.
- RD¯ is low only during opcode fetching; WR¯ remains high as no write operation occurs.
- S0=1, S1=1 during the opcode fetch cycle.
Memory Read Cycle
- The memory read cycle necessitates three T-States, from T1 to T3.
- ALE pin is activated during the first T-State.
- Data lines AD0-AD7 retrieve data from memory, with lower byte address stored.
- A8-A15 holds the higher byte of the address while IO/M¯ remains low for memory operations.
- RD¯ is low during the data fetching period; WR¯ is high indicating no write operation.
- S0=0, S1=1 for the memory read cycle.
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Description
Learn about control signals that transmit command and timing information among system modules. Explore timing signals indicating data and address information validity, as well as command signals specifying operations to be performed. Understand typical control lines like Memory write, Memory read, I/O write, and I/O read.
