Overview

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
• http//www.mhhe.com/patt2
• 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 x3100. Program starts
  at location x3000.

R1 ? x3100R3 ? 0 (Sum)R2 ? 12(count)
R20?
R4 ? MR1 R3 ? R3R4R1 ? R11 R2 ? R2-1
NO
YES
Write program
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Sum integers from x3100 x310B
Address Instruction Comments
x3000 1 1 1 0 0 0 1 0 1 1 1 1 1 1 1 1 R1 ? x3100
x3001 0 1 0 1 0 1 1 0 1 1 1 0 0 0 0 0 R3 ? 0
x3002 0 1 0 1 0 1 0 0 1 0 1 0 0 0 0 0 R2 ? 0
x3003 0 0 0 1 0 1 0 0 1 0 1 0 1 1 0 0 R2 ? 12
x3004 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 If Z, goto x300A
x3005 0 1 1 0 1 0 0 0 0 1 0 0 0 0 0 0 Load next value to R4
x3006 0 0 0 1 0 1 1 0 1 1 0 0 0 1 0 0 Add to R3
x3007 0 0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 Increment R1 (pointer)
X3008 0 0 0 1 0 1 0 0 1 0 1 1 1 1 1 1 Decrement R2 (counter)
x3009 0 0 0 0 1 1 1 1 1 1 1 1 1 0 1 0 Goto x3004
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The Add program in binary

• 0011000000000000 start x3000
• 1110001011111111 R1x3100
• 0101011011100000 R30
• 0101010010100000 R20
• 0001010010101100 R2R212
• 0000010000000101 If z goto x3009
• 0110100001000000 Load next value into R4
• 0001011011000100 R3R3R4
• 0001001001100001 R1R11
• 0001010010111111 R2R2-1
• 0000111111111010 goto x3004

6
The Add program in hex

• 3000 start x3000
• E2FF R1x3100
• 56E0 R30
• 54A0 R20
• 14AC R2R212
• 0405 If z goto x3009
• D840 Load next value into R4
• 16C4 R3R3R4
• 1261 R1R11
• 14BF R2R2-1
• 0FFA goto x3004

7
The Add program Data (hex)

• 3100 Begin data at x3100
• 3107 Loc x3100
• 2819
• 0110
• 0310
• 0110
• 1110
• 11B1
• 0019
• 0007
• 0004
• 0000
• 0000 Loc x310B

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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

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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.

Write program
15

Program to multiply R4 x R5 and place result
in R2
x3200 Clear Accumulator (R2) R2 lt- 0 x3201
Add R4 to Accumulator R2 lt- R2 R4
x3202 Dec R5 R5 lt- R5 1 x3203 Do
again if R5 gt 0 BR p x3201 x3204 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
x3200 Clear Accumulator (R2) R2 lt- 0 0101
010 010 1 00000 54A0 x3201 Add R4 to
Accumulator R2 lt- R2 R4 0001 010 010 0 00
100 1484 x3202 Dec R5 R5 lt- R5 1 0001
101 101 1 11111 1B7F x3203 Do again if
R5 gt 0 BR p x3201 0000 001 111111101
03FD x3204 Stop HALT 1111 0000 00100101
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 dont have
have a subtract instruction?
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Example - Occurrences of Inputted Char
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Example - Occurrences of Inputted CharProgram
(1 of 2)
Address Instruction Comments
x3000 0 1 0 1 0 1 0 0 1 0 1 0 0 0 0 0 R2 ? 0 (counter)
x3001 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1 0 R3 ? Mx3102 (ptr)
x3002 1 1 1 1 0 0 0 0 0 0 1 0 0 0 1 1 Input to R0 (TRAP x23)
x3003 0 1 1 0 0 0 1 0 1 1 0 0 0 0 0 0 R1 ? MR3
x3004 0 0 0 1 1 0 0 0 0 1 1 1 1 1 0 0 R4 ? R1 4 (EOT)
x3005 0 0 0 0 0 1 0 0 0 0 0 0 1 1 1 0 If Z, goto x300E
x3006 1 0 0 1 0 0 1 0 0 1 1 1 1 1 1 1 R1 ? NOT R1
x3007 0 0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 R1 ? R1 1
X3008 0 0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 R1 ? R1 R0
x3009 0 0 0 0 1 0 1 0 0 0 0 0 1 0 1 1 If N or P, goto x300B
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Example - Occurrences of Inputted CharProgram
(2 of 2)
Address Instruction Comments
x300A 0 0 0 1 0 1 0 0 1 0 1 0 0 0 0 1 R2 ? R2 1
x300B 0 0 0 1 0 1 1 0 1 1 1 0 0 0 0 1 R3 ? R3 1
x300C 0 1 1 0 0 0 1 0 1 1 0 0 0 0 0 0 R1 ? MR3
x300D 0 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 Goto x3004
x300E 0 0 1 0 0 0 0 0 0 0 0 1 0 0 1 1 R0 ? Mx3013
x300F 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 R0 ? R0 R2
x3010 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 1 Print R0 (TRAP x21)
x3011 1 1 1 1 0 0 0 0 0 0 1 0 0 1 0 1 HALT (TRAP x25)
X3012 Starting Address of File
x3013 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 ASCII x30 (0)