Memory Addressing Techniques in Computer Science

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Questions and Answers

Which instruction is used to store the content of the accumulator in memory?

STA (correct)

BUN

BSA

LDA

What is the primary function of the 'CLA' instruction?

Complement AC

Increment AC

Clear AC (correct)

Circulate right AC

Which of the following instructions would you use to branch unconditionally?

BUN (correct)

ISZ

STA

BSA

In a memory reference instruction, what does the 'Opcode' dictate?

The operation to be performed Signup and view all the answers

What does the 'INC' instruction do?

Increment AC Signup and view all the answers

Which instruction complements the content of the accumulator?

CMA Signup and view all the answers

What is the purpose of the 'ISZ' instruction?

Increment and skip if zero Signup and view all the answers

In a Register Reference Instruction, what does the bit pattern '1 1 1 1' indicate?

A register operation Signup and view all the answers

What part of the instruction code specifies the operation to be performed?

Opcode Signup and view all the answers

How many bits are needed to specify an address in a memory unit with 4096 words?

12 bits Signup and view all the answers

What is the maximum number of operations that can be specified with 4 bits for the opcode?

16 operations Signup and view all the answers

Where is the data operand read from during instruction execution?

Data portion of memory Signup and view all the answers

What role does the processor register (AC) play during instruction execution?

Acts as a temporary storage for data Signup and view all the answers

What is the purpose of the control unit in the memory organization?

To read and interpret operations Signup and view all the answers

What type of data is stored in the data portion of memory?

Operands Signup and view all the answers

Which of the following statements is correct about the organization of a computer's memory?

Each instruction code occupies 16 bits in memory. Signup and view all the answers

What does an instruction with an I bit set to 0 signify?

The instruction specifies a direct address. Signup and view all the answers

In which part of the instruction format is the opcode located?

In the first 3 bits Signup and view all the answers

How does the control unit recognize an indirect address instruction?

When the I bit is set to 1. Signup and view all the answers

Which of the following is true about the operand located at address 457?

It is found directly via the control unit for a specific ADD instruction. Signup and view all the answers

What distinguishes between a direct address and an indirect address in the instruction format?

The mode bit indicating 0 for direct and 1 for indirect. Signup and view all the answers

What does the binary string '00010100' represent in the instruction format?

The opcode for an ADD instruction. Signup and view all the answers

Which address mode is used when executing an instruction with an I bit set to 1?

Indirect address mode Signup and view all the answers

If an instruction specifies a binary equivalent of 300 and has the I bit set to 1, what type of instruction is it?

Indirect address instruction Signup and view all the answers

What needs to happen for an indirect address instruction to fetch an operand?

Two references to memory Signup and view all the answers

In the context of addressing memory, what does the address part in binary equivalent of 300 indicate?

The address of the operand Signup and view all the answers

What role does the Data Register (DR) play in the processor register's function?

Contains the memory operand Signup and view all the answers

How does the Program Counter (PC) function within the computer architecture?

Contains the address of the next instruction Signup and view all the answers

In an indirect addressing mode, which memory addresses need to be accessed?

First the address of the operand, then the operand itself Signup and view all the answers

Which register is used to hold the instruction code in a computer system?

Instruction Register Signup and view all the answers

What does the temporary register (TR) store during the computing process?

Intermediate data during operations Signup and view all the answers

What is the primary function of the accumulator (AC) in a computer system?

Carries out arithmetic and logic operations Signup and view all the answers

What type of data does the Output Register (OUTR) hold?

Output character Signup and view all the answers

Which register is responsible for holding the input character in a computer architecture?

Input Register Signup and view all the answers

What condition must be met for flip-flop R to be set to 1?

IEN must be 1 and either FGI or FGO must be 1 Signup and view all the answers

What happens at the end of the execute phase if R is equal to 1?

Control proceeds to an interrupt cycle Signup and view all the answers

Which timing signals indicate that flip-flop R cannot be set to 1?

T0, T1, T2 Signup and view all the answers

What is the purpose of the statement 'R  1' in the register transfer statements?

To initiate an interrupt cycle Signup and view all the answers

What occurs during the first timing signal in the interrupt cycle?

AR is cleared to 0 and PC is transferred to TR Signup and view all the answers

What does the register transfer statement RT1 accomplish?

It stores the return address in memory Signup and view all the answers

After the third timing signal, what is the new value of PC?

PC is incremented by 1 Signup and view all the answers

What will occur at the beginning of the next instruction cycle after the interrupt cycle?

Control goes back to T0 and resets SC Signup and view all the answers

Study Notes

Indirect Addressing

The binary equivalent of the address part is 300; it points to where the operand's address is stored.
Operand's address is 1350, where the actual operand is located.
Two memory references are required to fetch an operand: the first for the address of the operand, the second for the operand itself.
Indirect addressing acts as a pointer to an array of data found in memory.

Computer Registers

Program Counter (PC): Holds the address of the current instruction.
Address Register (AR): Holds the address for memory operations.
Instruction Register (IR): Holds the instruction code currently being executed.
Temporary Register (TR): Stores temporary data during operations.
Data Register (DR): Holds the memory operand for processing.
Accumulator (AC): Primary processor register for arithmetic operations.
Output Register (OUTR) and Input Register (INPR): Store output and input characters respectively.

Memory Specifications

Memory consists of 4096 words, with each word being 16 bits in size.
A common bus system connects various components of the computer for data transfer.

Instruction Types

Memory Reference Instructions: Carry an opcode and an address.
- Examples include operations like AND, ADD, LDA (load to AC), STA (store from AC), BUN (branch unconditionally), BSA (branch and save return address), ISZ (increment and skip if zero).
Register Reference Instructions: Target specific registers to perform operations.
- Examples include CLA (clear AC), CLE (clear E), CMA (complement AC), and INC (increment AC).
Input-Output Instructions: Manage data transfer between the computer and peripheral devices.

Instruction Format

Instruction format comprises an opcode and an address section.
For a memory with 4096 words, 12 bits are necessary for addressing, supporting 16 possible operations with 4 bits for opcodes.

Direct vs. Indirect Addressing

Direct Addressing: The instruction includes the operand's address directly.
Indirect Addressing: The instruction specifies a location holding the address of the operand.
The indirect address can be identified by a mode bit; a value of 0 indicates direct addressing, while 1 indicates indirect.

Control Flow

Instructions that require operand addresses can be fetched based on the type of addressing specified.
In direct addressing, the control retrieves and processes data from the specified address directly.
In indirect addressing, it first retrieves the address from a specified location, then accesses the operand.

Interrupt Cycle Operations

If both input and output flags are zero, the control continues to execute the next instruction.
When a flag is set while the Interrupt Enable (IEN) is active, the control shifts to an interrupt cycle.
The control assesses the flip-flop R at the end of the execute phase; if it's set, the next step is an interrupt cycle instead of a regular instruction cycle.

Register Transfer Statements

The interrupt cycle involves specific register transfer steps, including:
- Setting AR to zero and transferring PC content to TR.
- Storing the return address in memory and clearing PC.
- Incrementing PC, clearing IEN and R, and preparing to resume instruction execution.

Execution of Operations

The instruction cycle that fetches and executes takes place after the reset of the control during an interrupt cycle, bridging back into fetch operations for subsequent instructions.

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Description

This quiz explores the concept of indirect addressing in memory management. It covers how binary equivalents are used and the process involved in fetching operands from memory addresses. Test your understanding of memory addressing techniques and their implications in computing.