Instruction Medium

24 Questions

How many instructions does the MARIE ISA consist of?

13 instructions

What does the notation M[X] represent in the MARIE RTL?

The actual data value stored in memory location X

What does the SKIPCOND instruction do?

It skips the next instruction if the value in the AC is greater than zero

What is the hexadecimal representation of the SKIPCOND instruction with opcode 8 and bits 11 and 10 set to 10?

0x380

What is the purpose of the Accumulator (AC) register in MARIE?

To hold one operand of a two-operand instruction or the result of a conditional operation

Which register holds the memory address of an instruction or operand?

Memory Address Register (MAR)

What is the function of the Memory Buffer Register (MBR)?

To temporarily hold data before it is written to memory or after it is read from memory

What is the bit length of the instructions in MARIE?

16 bits

Which register holds data read from an input device?

Input Register (InREG)

What does the term 'byte ordering' or 'endianness' refer to in computer architecture?

The order in which bytes are stored in memory for multi-byte data types

In a big endian system, where is the most significant byte of a 32-bit integer stored in memory?

At the lowest memory address

What is the main advantage of a little endian memory organization over a big endian organization?

It makes it easier to place values on non-word boundaries

Suppose a computer uses 32-bit integers and the hexadecimal values 0xABCD1234, 0x00FE4321, and 0x10 are stored sequentially in memory starting at address 0x200. What would the value stored at address 0x200 be in a little endian system?

0x34

Which of the following is NOT a major consideration in computer architecture design related to memory organization?

Instruction format

What is the purpose of the `Getch` instruction in the first program?

To load a character from the address stored in Chptr

What will happen if the `Skipcond` instruction encounters a null character?

It will skip to the Jump instruction and jump to the address specified by Outp

In the second program, what is the purpose of the `Temp` register?

To store the value to be doubled

What is the purpose of the `JnS` instruction in the second program?

To jump to the Subr subroutine and store the return address

What is the purpose of the `JumpI` instruction in the `Subr` subroutine?

To jump to the return address stored in the memory location before Subr

What operation(s) can the ALU in MARIE perform?

Add, subtract, and clear

Which register in MARIE is enabled for reading when signals P0 and P1 are high?

MBR (Memory Buffer Register)

What signals need to be raised to copy the address part (X) of the IR to the MAR during the Add instruction?

P0, P1, and P2

What is the purpose of the LALT signal in MARIE?

To control the ALU's data source

Which signal needs to be raised to reset the counter in MARIE?

Study Notes

MARIE ISA

The MARIE ISA (Instruction Set Architecture) consists of only 13 instructions.

MARIE Instruction Format

The fundamental MARIE instructions have a specific format.
Each instruction consists of a 4-bit opcode and a 12-bit address.

Bit Pattern for LOAD Instruction

The opcode for the LOAD instruction is 1.
The address from which to load the data is specified in the instruction.

Bit Pattern for SKIPCOND Instruction

The opcode for the SKIPCOND instruction is 8.
Bits 11 and 10 are set to 10, indicating that the next instruction will be skipped if the value in the AC is greater than zero.
The hexadecimal representation of this instruction is not specified.

Microoperations

Each MARIE instruction consists of a sequence of smaller instructions called microoperations.
The exact sequence of microoperations can be specified using Register Transfer Language (RTL).

RTL for LOAD and ADD Instructions

The RTL for the LOAD instruction is: MAR ← X, MBR ← M[MAR], AC ← MBR.
The RTL for the ADD instruction is: MAR ← X, MBR ← M[MAR], AC ← AC + MBR.

MARIE Architecture

The MARIE architecture has the following characteristics:
Binary, two's complement data representation.
Stored program, fixed word length data and instructions.
4K words of word-addressable main memory.
16-bit data words.
16-bit instructions, with 4 bits for the opcode and 12 bits for the address.
A 16-bit Arithmetic Logic Unit (ALU).
Seven registers for control and data movement.

MARIE Registers

The seven MARIE registers are:
Accumulator (AC), a 16-bit register that holds a conditional operator or one operand of a two-operand instruction.
Memory Address Register (MAR), a 12-bit register that holds the memory address of an instruction or the operand of an instruction.
Memory Buffer Register (MBR), a 16-bit register that holds data after its retrieval from or before its placement in memory.
Program Counter (PC), a 12-bit register that holds the address of the next program instruction to be executed.
Instruction Register (IR), which holds an instruction immediately preceding its execution.
Input Register (InREG), an 8-bit register that holds data read from an input device.

Instruction Formats

Instruction formats are an important consideration in architecture design.
Two major formats are little-endian and big-endian.
Little-endian machines store the least significant byte first (at the lower address), while big-endian machines store the most significant byte first.

MARIE Assembly Programs

Examples of MARIE assembly programs are provided, including a program to print a string and a program to double the value stored at X.
These programs illustrate the use of MARIE instructions and registers.

Decoding and Control Signals

The register MBR is enabled for reading when P0 and P1 are high, and enabled for writing when P3 and P4 are high.
The ALU has only three operations: add, subtract, and clear.
The control signals for MARIE's Add instruction are specified.
The signal sequence for MARIE's Add instruction is: P3 P2 P1 P0 T3, P4 P3 T4 MR, Cr A0 P5 T5 LALT.

Explore the characteristics of the MARIE architecture, including binary data representation, fixed word length data, and instructions with a focus on main memory, data words, and instructions format.

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