1. LC-3 Assembly Language Programming Examples

2. Sample Program
Count the occurrences of a character in a file.

3. Count the occurrences of a character in a file (1 0f 2).;
; Program to count occurrences of a character in a file.
; Character to be input from the keyboard.
; Result to be displayed on the monitor.
; Program only works if no more than 9 occurrences are found.
; Initialization
.ORIG x3000
AND R2, R2, #0 ; R2 is counter, initially 0
LD R3, PTR ; R3 is pointer to character file
GETC ; R0 gets input character
LDR R1, R3, #0 ; R1 gets first character from file
; Test character for end of file
TEST ADD R4, R1, #-4 ; Test for EOT (ASCII x04)
BRz OUTPUT ; If done, prepare the output
; Test character for match. If a match, increment count.
NOT R1, R1
ADD R1, R1, R0 ; If match, R1 = xFFFF
NOT R1, R1 ; If match, R1 = x0000
BRnp GETCHAR ; If no match, do not increment
ADD R2, R2, #1
; Get next character from file.
GETCHAR ADD R3, R3, #1 ; Point to next character.
LDR R1, R3, #0 ; R1 gets next char to test
BRnzp TEST

4. Count the occurrences of a character in a file (2 of 2).;
; Output the count.
OUTPUT LD R0, ASCII ; Load the ASCII template
ADD R0, R0, R2 ; Covert binary count to ASCII
OUT ; ASCII code in R0 is displayed.
HALT ; Halt machine
; Storage for pointer and ASCII template
ASCII .FILL x0030 ; ASCII offset
PTR .FILL x4000 ; PTR to character file
.END

5. Programming Exercise #1
Write a program to add the contents of R0 and R1, and indicate in R2 if there
was an overflow
Flow Diagram
Assembly Code

6. Programming Exercise #1
; Add R3=R0+R1, R2=0 indicates no overflow ;
.ORIG x3000
AND R2, R2, #0 ;Initially R2=0 (no Overflow assumed)
ADD R3, R0, R1 ;R3=R0+R1
; test for overflow
ADD R0, R0, #0 ;test R0
BRN NEG ;Branch if RO negative
ADD R1, R1, #0 ;test R1
BRN DONE ;No overflow if operand signs differ (R1 NEG)
ADD R3, R3, #0 ;maybe, test R3
BRZP DONE ;No overflow if result sign matches (All POS)
ADD R2, R2, #1 ;R2=1 indicating overflow
NEG ADD R1, R1, #0 ;test R1
BRZP DONE ;No overflow if operand signs differ (R1 POS)
ADD R3, R3, #0 ;maybe, test R3
BRN DONE ;No overflow if result sign matches (All NEG)
ADD R2, R2, #1 ;R2=1 indicating overflow
DONE HALT
.END

7. Programming Exercise #2
Write a program to count the 1’s in register R0
Flow Diagram
Assembly code

8. Programming Exercise #2
; Program to count 1's in Register R0
; R3 is a working copy of R0
; R1 contains the count
; R2 is a loop counter
.orig x3100
ADD R3, R0, #0 ;copy R0 into R3
AND R1, R1, #0 ;clear count
ADD R3, R3, #0 ;test for Neg
BRZP NEXT ;count if Neg
ADD R1, R1, #1
NEXT AND R2, R2, #0 ;check remaining 15 bits
ADD R2, R2, #-15
LOOP ADD R3, R3, R3 ;shift R3 left
BRZP AGAIN ;count if Neg
AGAIN ADD R2, R2, #1 ;loop until done
BRN LOOP
HALT
.END

9. Programming Exercise #3
Write a program to add two, two digit numbers read from the console
Flow Diagram
Assembly code

10. Programming Exercise #3
; Program to add two 2 digit decimal numbers read from the console
; R1 & R2 are working registers to load 2 digit number
; R3 is first number
; R4 is second number
; R5 is the sum
; R6 is conversion offset
.orig x3600
LEA R0, MESSAGE ;print message
PUTS
; Get first number
LD R0, NEWLINE ;print PROMPT1
OUT
LEA R0, PROMPT1
GETC ;get first character
LD R6, M ;convert char to hex
ADD R0, R0, R6
ADD R1, R0, R0 ;R1 = 2xR0
ADD R2, R1, #0 ;copy R1 into R2
ADD R2, R2, R2 ;R2 = 4xR0
ADD R2, R2, R2 ;R2 = 8xR0
ADD R2, R2, R1 ;R2 = 10xR0
GETC ;get second character
ADD R0, R0, R6 ;convert to hex
ADD R3, R2, R0 ;R3 = first decimal number
; Get second number
LEA R0, PROMPT2 ;get first character
GETC
ADD R0, R0, R6 ;convert char to hex
GETC ;get second character
ADD R4, R2, R0 ;R4 = first decimal number

11. Programming Exercise #3 (2)
; Add the numbers and print results
ADD R5, R4, R3 ;R5 = R3 + R4
LEA R0, SUM ;prepare to print results
PUTS
LD R4, P ;find 1st digit
LD R3, M100
AND R0, R0, #0
LOOP1 ADD R0, R0, #1
ADD R5, R5, R3 ;subtract 100 until negative
BRZP LOOP1
ADD R5, R5, R4
ADD R0, R0, #-1
LD R6, P ;convert to ascii & print
ADD R0, R0, R6
OUT
AND R0, R0, #0 ;find 2nd digit
LOOP2 ADD R0, R0, #1
ADD R5, R5, #-10 ;subtract 10 until negative
BRZP LOOP2
ADD R5, R5, #10
ADD R0, R5, R6 ;convert and print 3rd digit
LD R0, NEWLINE
HALT
MESSAGE .STRINGZ "Enter two 2-digit decimal numbers:"
NEWLINE .FILL x000A
PROMPT1 .STRINGZ " The sum of "
PROMPT2 .STRINGZ " and "
SUM .STRINGZ " is "
M FILL xFFD0 ;-x30
P FILL X ; x30
M FILL xFF9C ;-100
P FILL x ; 100
.END

12. Programming Exercise #4
Write a program to read characters from the keyboard, echo them on the
console, and pack them into a file (2 characters per word)
Flow Diagram
Assembly code

13. HW, due 11/14/07
Write and test an LC-3 assembly language program to calculate and print all the numbers in the Fibonacci series that can be stored in words of the LC-3. The program should stop when it determines it has found the largest number.
Show:
A snapshot of your well commented Assembly program in the LC-3 Editor Window with the Assembly response.
A snapshot of the Simulator Console Display Window with the Fibonacci numbers displayed