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Computer Science 101
Homework Set 9
Due Wednesday, November 12
All homework should be turned in at class time and done in a neat fashion. You may
work together with one other person from the class (only one). If the work is exactly the
same for two people, turn in one paper with both names.
1. Here is a summary table of our assembly language for the hypothetical lab machine:
Assembly Language Table
Numeric
Assembly Language
Op Code
Mnemonic
0000
LOAD X
0001
STORE X
0010
CLEAR X
0011
ADD X
0100
INCREMENT X
0101
SUBTRACT X
0110
DECREMENT X
0111
COMPARE X
Numeric
Op Code
1000
1001
1010
1011
1100
1101
1110
1111
Assembly Language
Mnemonic
JUMP X
JUMPGT X
JUMPEQ
JUMPLT
JUMPNEQ X
IN X
OUT X
HALT
Assume that the first few memory cells of our hypothetical lab machine have the following contents:
Address (decimal)
Contents(binary)
0
0000000000000101
1
0101000000000110
2
0001000000000111
3
1110000000000111
4
1111000000000000
5
0000000000001001
6
0000000000000101
7
0000000000011010
Assume further that the machine is ready to begin the fetch-decode-execute cycle, that the PC holds
000000000001, and that the register R holds 9 (decimal). Note that we are not starting at the first
memory location.
a. Tell exactly what will be stored in each of the following locations at the end of the fetch phase (a
single fetch phase beginning with the situation described). Use decimal values for the PC, MAR,
MDR, R and memory locations. Use the usual instruction format for IR (not binary).
PC:
IR:
MAR:
MDR:
R:
Memory location 6:
b. Tell exactly what will be in these locations at the end of the execute phase (the single execute cycle
following the fetch phase of part a).
PC:
IR:
MAR:
MDR:
R:
Memory location 6:
c. Tell exactly what will be stored in these locations at the end of the next fetch.
PC:
IR:
MAR:
MDR:
R:
Memory location 6:
d. Tell exactly what will be stored in each of these locations at the end of the next execute phase.
PC:
IR:
MAR:
MDR:
R:
Memory location 6:
e. If we run the program, beginning at location 0, what will be the output?
These problems refer to the assembly language for the hypothetical lab machine.
First and foremost, your programs should be correct and follow the pseudocode. Extra
credit will be given for the “fastest” correct solutions, under the assumption that
execution of LOAD, STORE and CLEAR instructions take 2 units of time;
INCREMENT, DECREMENT, IN and OUT take 3 units of time; all other
instructions take 1 unit of time.
2. Using the pseudocode covered in the course or Python, write an algorithm to print out
the sum of three numbers entered by the user.
Now convert your pseudocode into a complete assembly language program, including
pseudo-operations.
3. Write a pseudocode or Python algorithm for a program that allows the user to input 100
numbers and prints the sum.
Convert your pseudocode into a complete assembly language program.
4. Convert the following algorithm into a complete assembly language program:
Set Ct to 0
Set ToGo to 100
While ToGo > 0 Do
Get Num
If Num > 0 Then
Set Ct to Ct + 1
Set ToGo to ToGo – 1
End-Of-Loop
Print Ct
Stop