1. CPSC 171 Introduction to Computer Science
Assembly Language and Assemblers

2. Machine Code Address Value 000000 1101 000101 000001 1101 000110 …
No natural language
Difficult to change
Data stored in binary

3. Assembly Language Symbolic Operations Symbolic Memory Addresses
Has Pseudo-operations for data generation

5. Structure of Assembly Code
Label: op-code symbol address label --comment

6. Example Assembly Code .begin loop: in x in y load x compare y
jumpgt done
out x
jump loop
done: out y
halt
x: .data 0
y: .data 0
.end

7. op-code Symbol REF: page 248, Fig 6.5
Arithmetic OpCodes
0000 load
0001 store
0010 clear
0011 add
0100 increment
0101 subtract
0110 decrement
I/0 OpCodes
1101 in
1110 out
Logic/Control OpCodes
0111 compare
1000 jump
1001 jumpgt
1010 jumpeq
1011 jumplt
1100 jumpneq
1111 halt

8. Convert Pseudocode to Assembly code
1. Set NegCount to 0
2. Set I to 1
3. While I ≤ 5 do lines 4 through 6
4. Input a number, N
5. if N < 0 then increment NegCount
6. Increment I
7. End of loop
8. Output NegCount
9. Stop

9. Assembly Code .begin loop: load FIVE compare I jumpgt finish in N
load N
compare NEG_ONE
jumplt dont_add
increment NegCount
dont_add: jump loop
finish: out NegCount
halt
NegCount: .data 0
I: .data 1
FIVE: .data 5
N: .data 0
NEG_ONE: .data -1
.end

10. You Try It Create Assembly Code for the following algorithm:
Get a number X
Get a number Y
If Y > X then
print out Y
Else
print out X
Stop