COSC 3332 HW3

Question 1

How many bits are required to address a 4M 16 main memory if

• main memory is byte addressable?
• main memory is word addressable?

Question 2

A digital computer has a memory unit with 32 bits per word. The instruction set consists of 110 different operations. All instructions have an operation code part (opcode) and two address fields: one for a memory address and one for a register address. This particular system includes eight general-purpose, user-addressable registers. Registers may be loaded directly from memory, and memory may be updated directly from the registers. Direct memory-to-memory data movement operations are not supported. Each instruction is stored in one word of memory.

• How many bits are needed for the opcode?
• How many bits are needed to specify the register?
• How many bits are left for the memory 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 3

Given the instruction set for MARIE in this chapter, do the following. Decipher the following MARIE machine language instructions (write the assembly language equivalent):

• 0010000000000111
• 1001000000001011
• 0011000000001001

Question 4

Write the following code segment in MARIEs assembly language:

if X > 1 then Y = X + X:
X = 0
end if;
Y = Y + 1

Question 5

What are the potential problems (perhaps more than one) with the following assembly language code fragment (implementing a subroutine) written to run on MARIE? The subroutine assumes the parameter to be passed is in the AC and should double this value. The Main part of the program includes a sample call to the subroutine. You can assume this fragment is part of a larger program.

Main, Load X
Jump Sub1
Sret, Store X
. . .
Sub1, Add X
Jump Sret

Question 6

Write the following code segment in MARIE assembly language:

X = 1;
While X < 10 do
X = X + 1;
Endwhile;