1. Overview Program in LC-3 machine language Use the Editor
Use LC-3 Simulator
Trap Instruction

2. LC-3 Editor / Simulator Go to Authors’ Web page: Download:
Download:
LC-3 Simulator – Win or Unix
- (LC-3 Edit, LC-3 Simulate)
LC-3 Simulator Lab Manual

3. Sum of 12 Integers Compute sum of 12 integers.
Numbers start at location x Program starts at location x3000.
R1  x3100 R3  0 (Sum) R2  12(count)
R2=0?
R4  M[R1] R3  R3+R4 R1  R1+1
R2  R2-1 NO
YES
Write program

4. Sum integers from x3100 – x310B Address Instruction Comments x3000
R1  x3100
x3001
R3  0
x3002
R2  0
x3003
R2  12
x3004
If Z, goto x300A
x3005
Load next value to R4
x3006
Add to R3
x3007
Increment R1 (pointer)
X3008
Decrement R2 (counter)
x3009
Goto x3004

5. The Add program in “binary”
;start x3000
;R1=x3100
;R3=0
;R2=0
;R2=R2+12
;If z goto x3009
;Load next value into R4
;R3=R3+R4
;R1=R1+1
;R2=R2-1
;goto x3004

6. The Add program in “hex”
3000 ;start x3000
E2FF ;R1=x3100
56E0 ;R3=0
54A0 ;R2=0
14AC ;R2=R2+12
0405 ;If z goto x3009
D840 ;Load next value into R4
16C4 ;R3=R3+R4
1261 ;R1=R1+1
14BF ;R2=R2-1
0FFA ;goto x3004

7. The Add program Data (hex)
3100 ; Begin data at x3100
3107 ; Loc x3100
2819
0110
0310
1110
11B1
0019
0007
0004
0000
0000 ; Loc x310B

8. LC3Edit Load the program into LC3Edit
- Store it as prog.bin for a binary file, or
Store it as prog.hex for a hex file
- Create a prog.obj file with the Editor
Load the data into LCEdit
- Store it as data.bin for a binary file, or
Store it as data.hex for a hex file
- Create a data.obj file with the Editor

9. LC-3 Simulator Open LC-3 Simulator - Load prog.obj - Load data.obj
- Set breakpoint(s)
- Step through program

10. TRAP Calls a service routine, identified by 8-bit “trap vector.”
When routine is done, PC is set to the instruction following TRAP.
vector
routine
x23
input a character from the keyboard
x21
output a character to the monitor
x25
halt the program

11. TRAPS

12. Add HALT to “Add” program
Add HALT statement and run program without breakpoint(s)

13. Example : Multiply
Write program to Multiply two unsigned integers in R4 and R5

14. Example : Multiply
This program multiplies two unsigned integers in R4 and R5.
clear R2
add R4 to R2
decrement R5
R5 = 0?
HALT No
Yes
Write program

15. Program to multiply [R4] x [R5] and place result in R2
x Clear Accumulator (R2) R2 <- 0
x Add [R4] to Accumulator R2 <- R2 + R4
x Dec R5 R5 <- R5 – 1
x Do again if [R5] > 0 BR p x3201
x Stop HALT

16. Program to multiply [R4] x [R5] and place result in R2
Code program

17. Program to multiply [R4] x [R5] and place result in R2
x Clear Accumulator (R2) R2 < A0
x Add [R4] to Accumulator R2 <- R2 + R
x Dec R5 R5 <- R5 – B7F
x Do again if [R5] > 0 BR p x FD
x Stop HALT F025
Test on Simulator

18. Write a program to place the absolute value of the [R2] in R2
How do we compute
A = - A
if we don’t have have a subtract instruction?

19. Example - # Occurrences of Inputted Char

20. Example - # Occurrences of Inputted Char Program (1 of 2)
Address
Instruction
Comments
x3000
R2  0 (counter)
x3001
R3  M[x3102] (ptr)
x3002
Input to R0 (TRAP x23)
x3003
R1  M[R3]
x3004
R4  R1 – 4 (EOT)
x3005
If Z, goto x300E
x3006
R1  NOT R1
x3007
R1  R1 + 1
X3008
R1  R1 + R0
x3009
If N or P, goto x300B

21. Example - # Occurrences of Inputted Char Program (2 of 2)
Address
Instruction
Comments
x300A
R2  R2 + 1
x300B
R3  R3 + 1
x300C
R1  M[R3]
x300D
Goto x3004
x300E
R0  M[x3013]
x300F
R0  R0 + R2
x3010
Print R0 (TRAP x21)
x3011
HALT (TRAP x25)
X3012
Starting Address of File
x3013
ASCII x30 (‘0’)