我必须为这个问题做一个LC-3代码，因为我是LC-3的新手，所以我遇到了一些麻烦：
编写一个LC-3汇编语言程序，执行以下操作：
1.向屏幕输出一条消息，提示用户输入LC-3汇编语言指令（如ADD）。用户按Enter/Return结束输入。
1.如果用户输入的指令是一条法律的LC-3汇编语言指令，程序将显示相应的4位操作码。例如，如果用户输入“ADD”，程序将打印出“0001”。
1.如果用户键入的指令不是法律的LC-3汇编语言指令（例如，“ADDD”），则程序将显示相应的错误消息。
1.显示输出后，程序循环回到顶部，重新初始化所有需要重新初始化的内容，然后再次执行。
1.当用户键入字符串“QUIT”并按Enter/Return键时，程序将退出。
下面是我的代码：

.ORIG x3000

; Constants for comparison
ADD_STR  .STRINGZ "ADD"
AND_STR  .STRINGZ "AND"
JMP_STR  .STRINGZ "JMP"
BR_STR   .STRINGZ "BR"
QUIT_STR .STRINGZ "QUIT"

; Memory locations
MESSAGE  .STRINGZ "Enter an LC-3 assembly language instruction (type QUIT to exit): "
USER_INPUT .BLKW #20

MAIN
    LEA R0, MESSAGE       ; Display the prompt message
    PUTS
    
    ; Read user input
    LEA R0, USER_INPUT    ; Store user input here
    GETC                  ; Read the first character
    OUT                   ; Echo the character

    ; Loop to read input until Enter/Return is pressed
    LOOP
        GETC              ; Read the next character
        OUT               ; Echo the character
        BRZ END_LOOP      ; Exit loop if Enter/Return is pressed
        STR R0, R1, #0    ; Store the character in memory
        ADD R1, R1, #1    ; Move to the next memory location
        BRNZP LOOP        ; Repeat the loop

    END_LOOP

    ; Compare user input to known instructions
    LEA R1, USER_INPUT    ; Load the input string pointer
    LEA R2, ADD_STR      ; Load ADD instruction pointer
    LEA R3, AND_STR      ; Load AND instruction pointer
    LEA R4, JMP_STR      ; Load JMP instruction pointer
    LEA R5, BR_STR       ; Load BR instruction pointer
    LEA R6, QUIT_STR     ; Load QUIT instruction pointer
    
    ; Compare input with ADD
    CMP_ADD
        LDR R7, R1, #0   ; Load a character from input
        LDR R0, R2, #0   ; Load a character from ADD string
        NOT R0, R0       ; Get the 2's complement of ADD character
        ADD R0, R0, #1   ; Add 1 to compare with input character
        ADD R7, R7, #1   ; Prepare to compare next character
        BRnp ADD_CHECK   ; Check condition

    ADD_CHECK
        BRz IS_ADD       ; If both characters match, it's ADD instruction
        BRnzp CMP_AND    ; Else, check for AND instruction

    IS_ADD
        ; Display the opcode for ADD
        LEA R0, ADD_STR  ; Load ADD instruction string
        PUTS             ; Display it
        BRnzp MAIN       ; Go back to the main loop

    CMP_AND
        ; Similar comparison process for AND
        ; ... (Repeat the above process for AND, JMP, BR, QUIT)

    ; Handling for other instructions and errors can be written similarly

    ; Handle QUIT instruction
    QUIT_CHECK
        ; ...

    ; Other instruction checks and error messages go here

    ; Loop back to the beginning
    BRnzp MAIN

.END

字符串
问题是程序没有正确处理用户的输入，“Enter an LC-3 assembly language instruction（type QUIT to exit）：is printed but when I try put（e.g. ADD）nothing is returned，以及不工作的QUIT指令. Also I'm not sure how to finish up with my code for this project. I hope someone can help me out. Thanks.