LC-3 output streaming random characters - output

Question

I have been writing this program in assimbly language that encrypts or decrypts a string of text. At the end it should be simply outputting the encoded message but instead I am just getting a massive number of random characters. Anyone have any idea whats going on here?
.ORIG x3000
;CLEAR REGISTERS
AGAIN AND R0, R0, 0 ;CLEAR R0
AND R1, R1, 0 ;CLEAR R1
AND R2, R2, 0 ;CLEAR R2
AND R3, R3, 0 ;CLEAR R3
AND R4, R4, 0 ;CLEAR R4
AND R5, R5, 0 ;CLEAR R5
AND R6, R6, 0 ;CLEAR R6
;ENCRYPT/DECRYPT PROMPT
LEA R0, PROMPT_E ;LOADS PROMPT_E INTO R0
PUTS ;PRINTS R0
GETC ;GETS INPUT
OUT ;ECHO TO SCREEN
STI R0, MEMX3100 ;X3100 <- R0
;KEY PROMPT
LEA R0, PROMPT_K ;LOADS PROMPT_E INTO R0
PUTS ;PRINTS R0
GETC ;GETS INPUT
OUT ;ECHO TO SCREEN
STI R0, CYPHERKEY ;X3101 <- R0
;MESSAGE PROMPT
LD R6, MEMX3102 ;R6 <- MEMX3102
LEA R0, PROMPT_M ;LOADS PROMPT_E INTO R0
PUTS ;PRINTS R0
LOOP1 GETC ;GETS INPUT
OUT ;ECHO TO SCREEN
ADD R1, R0, #-10 ;R1 <- R0-10
BRZ NEXT ;BRANCH NEXT IF ENTER
STR R0, R6, #0 ;X3102 <- R0
ADD R6, R6, #1 ;INCRIMENT COUT
LD R2, NUM21 ;R2 <- -12546
ADD R5, R6, R2 ;R5 - R2
STI R5, MEMX4000 ;MEMX4000 <- R5
LD R1, NUM20 ;R1 <- NUM20
ADD R1, R6, R1 ;CHECK FOR 20
BRN LOOP1 ;CREATES WHILE LOOP
;Function choose
NEXT LDI R6, MEMX3100 ;R6 <- X3100
LD R1, NUM68 ;R1 <- -68
ADD R1, R6, R1 ;CHECKS FOR D INPUT
BRZ DECRYPT
;ENCRYPT FUNCTION(DEFAULT)
LD R4, MEMX3102 ;R6 <- X3102
LOOP2 LDR R1, R4, #0 ;R1 <- MEM[R4+0]
LDI R5, ASCII ;R5 <- ASCII
ADD R1, R1, R5 ;STRIPS ASCII
AND R6, R1, #1 ;R6 <- R1 AND #1
BRZ LSBOI ;BRANCH IF LSB = 0
ADD R1, R1, #-1 ;R1 <- R1-1
BRNZP KEYLOAD ;BRANCH TO KEYLOAD
LSBOI ADD R1, R1, #1 ;R1 <- R1+1
KEYLOAD LDI R2, CYPHERKEY ;R2 <- CYPHERKEY
ADD R1, R1, R2 ;R1 <- R1+R2
STR R1, R4, #21 ;MEM[R4+21] <- R1
ADD R4, R4, #1 ;R4 <- R4 + 1
LD R5, MEMX4000 ;R5 <- COUNT
NOT R5, R5 ;NOT R5
ADD R5, R5, R4 ;CHECK FOR NEGATIVE
BRN LOOP2 ;LOOP
BRNZP NEXT2 ;BRANCH WHEN DONE
;DECRYPT FUNCTION DECRYPT LD R4, MEMX3102 ;R4 <- X3102 LOOP3 LDR R1, R4, #0 ;R1 <- MEM[R4+0] LDI R5, ASCII ;R5 <- ASCII ADD R1, R1, R5 ;STRIPS ASCII LDI R2, CYPHERKEY ;R2 <- CYPHERKEY NOT R2, R2 ;R2 <- NOT R2 ADD R1, R1, R2 ;R1 <- R1 - CYPHERKEY AND R6, R1,
#1 ;R6 <- R1 AND #1 BRZ LSBOI2 ;BRANCH IF LSB = 0 ADD R1, R1, #-1 ;R1 <- R1-1 BRNZP NEXTTASK1 ;BRANCH TO KEYLOAD LSBOI2 ADD R1, R1, #1 ;R1 <- R1+1 NEXTTASK1 STR R1, R4, #21 ;MEM[R4+21] <- R1 ADD R4, R4, #1 ;R4 <- R4 + 1 LD R5, MEMX4000 ;R5 <- COUNT NOT R5, R5 ;NOT R5 ADD R5, R5, R4 ;CHECK FOR NEGATIVE BRN LOOP3 ;LOOP
;OUTPUT NEXT2 LD R4, MEMX3102 ;R4 <- X3102 LOOP4 LDR R0, R4,
#21 ;R0 <- [R4+21] OUT ;PRINT R0 ADD R4, R4, #1 ;R4 <- R4+1 LD R5, MEMX4000 ;R5 <- COUNT NOT R5, R5 ;NOT R5 ADD R5, R5, R4 ;CHECK FOR NEGATIVE BRN LOOP4
HALT MEMX4000 .FILL X4000 ASCII .FILL #-30 NUM21 .FILL #-12546 NUM20 .FILL #-12566 MEMX3102 .FILL X3102 CYPHERKEY .FILL X3101 MEMX3100 .FILL X3100 NUM68 .FILL #-68 NUM32 .FILL #-32 PROMPT_E .STRINGZ "\nTYPE E TO ENCRYPT OR TYPE D TO DECRYPT (UPPER CASE): " PROMPT_K .STRINGZ "\nENTER THE ENCRYPTION KEY (A SINGLE DIGIT FROM 1 TO 9) " PROMPT_M .STRINGZ "\nINPUT A MESSAGE OF NO MORE THAN 20 CHARACTERS THEN PRESS <ENTER> "
.END

Answer 1

There are a number of different things that are going on in your program, here are some of the things I've found:
Encoding loop loops more times than the number of characters entered
The encryption key is stored and used in its ASCII form
characters from the user are stored in the middle of the PROMPT_M text
encoding loop cycles for thousands of times
Encoding loop didn't change any of the stored characters at location x3102
Output routine doesn't loop, so it only outputs one char
From what I've seen your program takes a non ascii char from the user adds it to the ascii form of the encryption key and then stores that hundreds of times at every memory offset 21 locations from x3102. When your output routine runs it pulls the value stored at x3117 and outputs that one char, then halts the program.