Sarajevo School of Science and Technology
Course: CS130, Fall 2005.
Assignment #3: given Dec 20, due Tuesday Dec 27, 2005, 3:00 PM.
Show your answers in the space below question. Copying and mess will be punished.
Question 1 The PC contains x3010. The following memory locations contain values
as shown:
x3050:
x70A4
x70A2:
x70A3
x70A3:
xFFFF
x70A4:
x123B
The following three instructions are then executed.
x3010
1110 0110 0011 1111 LEA R3, x3F
x3011
0110 1000 1100 0000 LDR R4, R3, #0
x3012
0110 1101 0000 0000 LDR R6, R4, #0
; R3 <- x3050
; R4 <- x70A4
; R6 <- x123B
a. What is the content of R6 register? (10 points)
x123B
b. Replace three above instructions with the single one with the same effect.
(10 points)
LDI R6, x3F; 1010 1100 00111111 ; R6 <- M[M[x3050] = M[x70A4] = x123B
c. What is a difference between this question and textbook problem 5.22?
(5 points)
x3010 LEA R6, x3F
; R6 <- x3050
x3011 LDR R4, R3, #0
; R4 <- ????
x3012 LDR R6, R4, #0
; R6 <- ????
Question 2 Problem 6.15: Below are register and memory contents before and after
the instruction at x3010 is executed. Indicate the instruction in mnemonic and
binary format. (10 points)
register
R0:
R1
R2
R3
R4
R5
R6
R7
x3010
before
x3208
x2D7C
xE373
x2053
x33FF
xF4A2
x5220
x3208
after
x3208
x2D7C
xE373
x2053
x33FF
xF4A2
x5220
x3208
STR R2, R4, #7
memory
x3400
x3401
x3402
x3403
x3404
x3405
x3406
x3407
before
x3001
x7A00
x7A2B
xA700
xF011
x2003
x31BA
xC100
after
x3001
x7A00
x7A2B
xA700
xF011
x2003
xE373
xC100
x3010 0111 010 100 000111 ; M[R4 + 7] <- R2
Question 3 Problem 9.4: Consider the following LC-3 program:
.ORIG
x3000
L1
LEA R1, L1
AND R2, R2, x0
ADD R2, R2, x2
LD
R3, P1
L2
LDR R0, R1, xC
OUT
ADD R3, R3, #-1
BRz GLUE
ADD R1, R1, R2
BR
L2
GLUE
HALT
P1
.FILL xA
.STRINGZ "Ixnasetfrvujchtio!r"
.END
a. After this program is assembled and loaded what binary pattern is stored in
memory location x3005? (5 points) TRAP x21 = 1111 0000 0010 0001
b. Which instruction (provide memory address) is executed after instruction
x3005 is executed? (10 points) x0430 ST R1, SaveR1 ; 0011 001 000000111
c. Which instruction (provide memory address) is executed prior to instruction
x3006? (5 points)
x0435
RET ; 1100 000 111 000000
d. What is the output of this program? (5 points) Instructor
Question 4 Write an LC-3 assembly program that will take your full name as an
input up to 30 characters and after you hit “return” ‘0A’ it will echo your name to
the console followed by “the Great”. For instance when I hit return after typing
Dino Melin, the program will print: Dino Melin the Great. (30 points)
You have to show your program working to the Teaching Assistant to get points.
You can use TRAPS x20 and x22 as well.
Question 5 Problem 10.3: Push Rn pushes Register n onto stack, POP Rn removes a
value from the stack and loads it into Rn. Figure below shows a snapshot of the
eight registers of the LC-3 before and after the following six stack operations are
performed. Identify (a) – (d). (10 points).
Before
After
R0 x0000 PUSH R4
R0 x1111
PUSH R4
R1 x1111 PUSH (a)
R1 x1111
PUSH R1
R2 x2222 POP (b)
R2 x3333
POP R0
R3 x3333 PUSH (c)
R3 x3333
PUSH R3
R4 x4444 POP R2
R4 x4444
POP R2
R5 x5555 POP (d)
R5 x5555
POP R7
R6 x6666
R6 x6666
R7 x7777
R7 x4444