# Assignment 2: MARIE and ISA solution

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## Description

5/5 - (1 vote)

Question 1:

A digital computer has a memory unit with 16 bits per word. The instruction set consists of 122 different operations. All instructions have an operation code part (opcode) and an address part (allowing for only one address). Each instruction is stored in one word of memory. [10 marks]

How many bits are needed for the opcode?
How many bits are left for the address part of the instruction?
What is the maximum allowable size for memory?
What is the largest unsigned binary number that can be accommodated in one word of memory?

Question 2:

Consider an instruction Add 1000. Memory contents, Accumulator (AC), and R1 Register contents are depicted in the below figure: (such as memory address 1000 contains a value 1400, memory address 1100 contains a value 400 etc. All the numbers used here are decimals.) [8 marks]

Assuming R1 is implied in the indexed addressing mode, determine the actual value loaded into the accumulator (AC) using the following addressing modes:

Immediate
Direct
Indirect
Indexed

Question 3:

More registers appears to be a good thing, in terms of reducing the total number of memory accesses a program might require. Using the arithmetic expression S = (A+B)-(C+D), support this statement. [Hints: First, determine the number of memory accesses necessary using MARIE and the two registers for holding memory data values (AC and MBR). Then perform the same arithmetic computation for a processor that has more than three registers (for example, R1, R2, R3, R4) to hold memory data values.] [6 marks]

Question 4:

Assemble the MARIE program below. [6 marks]

102 STORE D

103 CLEAR

104 OUTPUT

106 STORE B

107 HALT

108 A, HEX 00FC

109 B, DEC 14

10A C, HEX 0108

10B D, HEX 0000

a) List the hexadecimal code for each instruction [2 marks]

b) Draw the symbol table [2 marks]

c) What is the value stored in the AC when the program terminates? [2 marks]

Rationale

This assessment task will assess the following learning outcome/s:

be able to investigate the internal operation of the Central Processing Unit (CPU) and describe how it is used to execute instructions.
be able to investigate and describe in detail the essential elements of computer organisation including internal bus, memory, Input/Output ( I/O) organisations and interfacing standards and discuss how these elements function.
This assessment task covers topics on CPU operation and Instruction Set Architecture, and has been designed to ensure that you are engaging with the subject content on a regular basis.

Marking criteria and standards

Criteria
HD (85%-100%)
DI (75%-84%)
CR (65%-74%)
PS (50%-64%)
FL (0%-49%)
Correct Calculation in Q1 and Q2
Answers are correct and clearly show the calculations
Answers are correct, an omission of few calculations.
Answers are correct, an omission of many calculations.
Student demonstrates the understanding, however, the calculations are incorrect.
Incorrect answer with no demonstration of understanding the topic.
Correct steps in assembly code in Q3
Assembly Program is correct and clearly show the steps
Assembly Program is correct, an omission of few steps
Assembly Program is correct, an omission of many steps
Student demonstrate the understanding in writing assembly program related to each architecture, however, the steps are incorrect.
Incorrect program with no demonstration of understanding the topic.
Answers are correct in a, b, and c
Answers are correct, omission of one of three branches
Answers are correct, an omission of two of three branches
Student demonstrates the understanding, however, the results in 3 branches are incorrect.
Incorrect program with no demonstration of understanding the topic.

Total marks available = 5 marks ·

Subtract the marks are set in marking criteria for each incorrect or missing instruction value in the code assembly;

Subtract 1 mark for each incorrect or missing symbol;

Presentation

File naming convention: When you upload files to the TURNITIN for this subject, please use SUBJECT CODE, SURNAME, STUDENT ID, ASSESSMENT NUMBER, SESSION. For example – ITC544 PATEL 11554466 A2 201860.doc