我认为问题出在最后一部分。这将从ds:si复制字节到es:di，从ds:160开始，并向上移动内存，因为方向标志已清除cld。一些随机的字符和颜色出现在屏幕上。

clear_screen:
    mov ax,0b800h
    mov es,ax
    mov ax,0
    mov di,ax
    mov ax,160
    mov si,ax
    cld
    mov cx,24*80
    rep movsw

    ret      ; add return

如果你想使用上面的代码，嗯，也许添加clearBuffer dw 80*24 dup(0)，然后从clearBuffer复制字节到es:di (B800h)。但这会增加项目规模。

clear_screen:
    mov ax,0b800h
    mov es,ax
    mov ax,0
    mov di,ax
   
    mov si,offset clearBuffer
    cld
    mov cx,24*80
    rep movsw

    ret      ; add return

我认为更好的方法是复制立即值到vram。

clear_screen:
        mov ax,0b800h
        mov es,ax           ; es = b800h
        mov ax,0700h        ; ah = character's attribute, al = character
        mov di,0            ; di = 0    
        cld             
        mov cx,25*80
        rep stosw           ; copy from ax to es:di
    
        ret

REMOVE int 10h after every call to clear_screen。这将消除屏幕上的大字母。

UPDATE

好吧，我深入研究代码…
1.我添加了set_cursor_0_0以将光标设置为0，0坐标。每次用户输入后重置。以保持屏幕上的东西干净漂亮。
1.背景为蓝色，前景为白色。
1.返回文本模式，将属性重置为正常。
1.下面是完整的代码

.model small
.stack 64

.data
     newline     db 13,10,'$'       ; Added
    welcome     db  "Welcome to Penang Travel Bus System!: $"
    msg1        db  10,13, "Pick up destinations : $"
    msg2        db  10,13, "Drop up destinations : $"
    pickupTitle db  10,13, "---- Your Pickup Destination ---- $"
    dropoffTitle    db  10,13, "---- Your Drop-off Destination ---- $"
    destination1    db  10,13, "1. Spice Arena Bayan Lepas $"
    destination2    db  10,13, "2. Ayer Itam Bus Terminal $"
    destination3    db  10,13, "3. Komtar Sentral Georgetown $"
    destination4    db  10,13, "4. Balik Pulau Bus Terminal $"
    destination5    db  10,13, "5. Gurney Plaza Pulau Tikus $"
    destination6    db  10,13, "6. Vantage Point Bus Stop Tanjung Tokong $"
    pickupPrompt    db  10,13,10,13, "Enter the number of your pickup destination (1-6): $"
    dropoffPrompt   db  10,13,10,13, "Enter the number of your drop-off destination (1-6): $"
    pickupChoice    db  ?  
    dropoffChoice   db  ?
    pickupchosen    db  10,13, "You selected pickup destination: $"
    dropoffchosen   db  10,13,  "You selected drop-off destination: $"
    invalid_pickup  db  10,13, "Invalid pickup destination. Please select from (1-6): $"
    invalid_dropoff db  10,13, "Invalid drop-off destination. Please select from(1-6): $"
    invalid_destination db 10,13,"Your drop-off destination cannot be same as your pickup destination. Please select other destination: $"
    invalid_quantity db 10,13, "Invalid quantity. Minimum number of tickets is 0 and maximum is 9. Please select from (1-9): $"
    invalid_feature db 10,13, "Invalid feature. Enter from (1-4) or (0) for no features. $"
    quantityPrompt  db  10,13,10,13, "Enter the quantity of tickets (1-9): $"
    ticketQuantity  db ?
    features    db  10,13,10,13, "Would you like any of these extra features? $"
    snacks      db  10,13, "1. Snacks of your choice: (Twisties / Super Ring / Cheezels / Chips) - RM7.00 $"
    beverages   db  10,13, "2. Cold beverages (100Plus / Cola / 7UP / Sprite) - RM7.00 $"
    entertainment   db  10,13, "3. TV Entertainment (Smart TV) - RM10.00 $"
    wifi        db  10,13, "4. Onboard WiFi - RM8.00 $"
    featuresPrompt db 10,13, "Enter the features you want (1-4) Press (0) if no : $"
    featuresChoice db 0
    featuremessage  db  10,10, "Feature added. Would you like any more features? $"
    chosenfeatures db 10,13, "Feature chosen: $"

;==========================================================================

.code
    mov ax,0003h                ; Added
    int 10h                     ; Added
   
    main proc far

    mov ax , @data
    mov ds , ax 
    
   call clear_screen            ; Added
    call set_cursor_0_0         ; Added

    mov ah , 09h
    lea dx , welcome
    int 21h
    
    mov ah , 09h                ; Added
    lea dx , newline            ; Added
    int 21h                 ; Added
;==============================================================
    
Pickup:                         ; Added 
                                ; this starts Pickup part
    mov ah , 09h
    lea dx , pickupTitle
    int 21h

    mov ah , 09h
    lea dx , msg1
    int 21h

    mov ah , 09h
    lea dx , destination1
    int 21h

    mov ah , 09h
    lea dx , destination2
    int 21h

    mov ah , 09h
    lea dx , destination3
    int 21h

    mov ah , 09h
    lea dx , destination4
    int 21h

    mov ah , 09h
    lea dx , destination5
    int 21h

    mov ah , 09h
    lea dx , destination6
    int 21h
    
    mov ah , 09h
    lea dx , pickupPrompt
    int 21h

    ;Read user input for pickup choice
get_pickup:
    mov ah , 01h            ; Please prepare I want to read a char
    int 21h
    sub al , 30h            ; Change it to integer
    
    cmp al , 1
    jl invalidpickup
    cmp al , 6
    jg invalidpickup
    
    mov pickupChoice, al
    jmp Dropoff             ; Changed
                                ; Pickup and Dropoff labels
                                ; marks start of next phase

invalidpickup:              ; Display an invalid pickup message if user doesn't enter from 1 to 6
    mov ah , 09h
    lea dx , invalid_pickup
    int 21h
    jmp get_pickup

;Dropoff menu

Dropoff:                        ; Added
   call clear_screen            ; Added
    call set_cursor_0_0         ; Added
    
    mov ah , 09h
    lea dx, dropoffTitle    ; Display the title
    int 21h

    mov ah , 09h
    lea dx, destination1    ; Display drop-off 1
    int 21h
        
    mov ah , 09h
    lea dx , destination2   ; Display drop-off 2
    int 21h

    mov ah, 09h
    lea dx , destination3   ; Display drop-off 3
    int 21h

    mov ah , 09h
    lea dx , destination4   ; Display drop-off 4
    int 21h

    mov ah , 09h
    lea dx , destination5   ; Display drop-off 5
    int 21h

    mov ah , 09h
    lea dx , destination6   ; Display drop-off 6
    int 21h
        
    mov ah , 09h
    lea dx , dropoffPrompt
    int 21h
    
get_dropoff:                    ; Added
                                ; labels get_pickup and get_dropoff
                                ; want input from user
    mov ah , 01h            ; Please prepare I want to read a char
    int 21h
    sub al , 30h            ; Change it to integer

    cmp al , 1              ; If user doesn't enter (1-6) it shows an error message
    jl invaliddropoff
    cmp al , 6
    jg invaliddropoff

    mov dropoffChoice , al  ; Protect the input

;We also need to check if the dropoff choice is the same as pickup
;Need to load to register to only use cmp

    mov al , pickupChoice
    cmp al , dropoffChoice
    je invaliddestination
                              ; Removed
                              ; Value pickupChoice is in memory already
                        ; no need to save this again                              
   ; mov pickupChoice , al   ; Move it back to the variable

    jmp destination

invaliddropoff:             ; Error message and loop back to get user input

    mov ah , 09h
    lea dx , invalid_dropoff
    int 21h
    jmp get_dropoff

invaliddestination:         ; Error message if user enters same destination for pickup and dropoff
    mov ah , 09h
   lea dx , invalid_destination
   int 21h
   jmp get_dropoff

destination:
    call clear_screen           ; Added
    call set_cursor_0_0         ; Added

    mov ah , 09h
   lea dx , pickupchosen
   int 21h

   mov dl , pickupChoice
   add dl , 30h
   mov ah , 02h
   int 21h

   mov ah , 09h
   lea dx , dropoffchosen
   int 21h

   mov dl , dropoffChoice
   add dl , 30h
   mov ah , 02h
   int 21h

; Prompt for the quantity of tickets

   mov al , 0          ; Clear the al register just in case

get_ticketquantity:
    mov ah , 09h
    lea dx , quantityPrompt
    int 21h

; Read user input for quantity

    mov ah , 01h
    int 21h
    sub al , 30h            ; Change to integer
 
; Check if the quantity is valid (between 1 and 9)

    cmp al , 1
    jl invalidquantity
    cmp al , 9
    jg invalidquantity

    mov ticketQuantity, al      ; Protect the value
    jmp extrafeatures

    invalidquantity:

    mov ah , 09h
    lea dx, invalid_quantity    ; Display error message for invalid quantity
    int 21h

    jmp get_ticketquantity      ; Repeat the loop to get a valid quantity

extrafeatures:
    call clear_screen           ; Added
    call set_cursor_0_0         ; Added
    
extrafeaturesadded:             ; Added
    
;Code to display any extra features the user may input
    mov ah , 09h
    lea dx , features
    int 21h

    mov ah , 09h
    lea dx , snacks
    int 21h

    mov ah , 09h
    lea dx , beverages
    int 21h

    mov ah , 09h
    lea dx , entertainment
    int 21h

    mov ah , 09h
    lea dx , wifi
    int 21h

    mov ah , 09h
    lea dx , featuresprompt
    int 21h

    mov ah , 01h
    int 21h
    sub al , 30h                    ; Protect the input

    cmp al , 0
    je displayfeatures              ; Jump to displayfeatures if user enters 0
    cmp al , 1
    je addsnacks
    cmp al , 2
    je addbeverages
    cmp al , 3
    je addentertainment
    cmp al , 4
    je addwifi

    jmp invalidfeature

    addsnacks:
    or featuresChoice, 1            ; If user chooses snacks, the corresponding bit is set (bit 1)
    call clear_screen                   ; Clear screen and let user to choose anymore extra features
     call set_cursor_0_0            ; Added 
   ; int 10h
    mov ah , 09h
    lea dx , featuremessage
    int 21h
    jmp extrafeaturesadded

    addbeverages:
    or featuresChoice, 2            ; If user chooses beverages, the corresponding bit is set (bit 2)
    call clear_screen                       ; Clear screen and let user to choose anymore extra features
     call set_cursor_0_0            ; Added 
    ;int 10h
    mov ah , 09h
    lea dx , featuremessage
    int 21h
    jmp extrafeaturesadded

    addentertainment:
    or featuresChoice, 4            ; If user chooses entertainment, the corresponding bit is set (bit 3)
    call clear_screen                   ; Clear screen and let user to choose anymore extra features
     call set_cursor_0_0            ; Added 
    ;int 10h
    mov ah , 09h
    lea dx , featuremessage
    int 21h
    jmp extrafeaturesadded

    addwifi:
    or featuresChoice, 8            ; If user chooses wifi, the corresponding bit is set (bit 4)
    call clear_screen                       ; Clear screen and let user to choose anymore extra features
     call set_cursor_0_0            ; Added 
    ;int 10h
    mov ah , 09h
    lea dx , featuremessage
    int 21h
    jmp extrafeaturesadded

    invalidfeature:
    cmp al , 1
    jne validfeature                ; If true , jump to valid feature option that 
                                    ; repeats without showing invalid feature message
    call clear_screen                   ; Clear screen and let user to choose anymore extra features
    ;int 10h

    mov ah , 09h                    ; If it didn't jump , this error message will appear
    lea dx , invalid_feature
    int 21h
    jmp extrafeaturesadded

    validfeature:                   ; If the jump occured it will just loop back as normal
    jmp extrafeaturesadded

displayfeatures:
    jmp finaldisplay                ; Jump to final display

finaldisplay:
    call clear_screen                   ; Clear screen and summarize the user order
     call set_cursor_0_0            ; Added     
  ;  int 10h 
        
    mov ah , 09h
    lea dx , pickupchosen
    int 21h

    mov dl , pickupChoice
    add dl , 30h
    mov ah , 02h
    int 21h

    mov ah , 09h
    lea dx , dropoffchosen
    int 21h

    mov dl , dropoffChoice
    add dl , 30h
    mov ah , 02h
    int 21h

    mov ah  , 09h
    lea dx , quantityPrompt
    int 21h

    mov dl , ticketQuantity
    add dl , 30h
    mov ah , 02h
    int 21h

    mov ah , 09h
    lea dx , chosenfeatures
    int 21h

    ; Check snacks
    mov ah , 0
    mov al , featuresChoice
    and al , 1    ; Check the least significant bit (snacks)
    cmp al , 1
    je snacks_chosen
    jmp beverages_check

snacks_chosen:
    mov ah , 09h
    lea dx , snacks
    int 21h
    jmp beverages_check

beverages_check:
    ; Check beverages (bit 1)
    mov ah , 0
    mov al , featuresChoice
    and al , 2    ; Check bit 1 (beverages)
    cmp al , 2
    je beverages_chosen
    jmp entertainment_check

beverages_chosen:
    mov ah , 09h
    lea dx , beverages
    int 21h
    jmp entertainment_check

entertainment_check:
    ; Check entertainment (bit 2)
    mov ah , 0
    mov al , featuresChoice
    and al , 4    ; Check bit 2 (entertainment)
    cmp al , 4
    je entertainment_chosen
    jmp wifi_check

entertainment_chosen:
    mov ah , 09h
    lea dx , entertainment
    int 21h
    jmp wifi_check

wifi_check:
    ; Check WiFi (bit 3)
    mov ah , 0
    mov al , featuresChoice
    and al , 8    ; Check bit 3 (WiFi)
    cmp al , 8
    je wifi_chosen
    jmp final

wifi_chosen:
    mov ah , 09h
    lea dx , wifi
    int 21h
    jmp final

final:
    mov ah,8                    ; w8 4 key to read messages
    int 21h
    
    mov ax,0003h                ; Added
    int 10h                     ; Added 
   
   mov ax , 4c00h
   int 21h

    main    endp
    
    clear_screen:
        mov ax,0b800h
        mov es,ax           ; es = b800h
        mov ax,1F00h        ; ah = character's attribute, al = character
                            ; white on blue
        mov di,0            ; di = 0    
        cld             
        mov cx,25*80
        rep stosw           ; copy from ax to es:di 
        ret
        
    set_cursor_0_0:
        mov ah,02h
        mov dx,0
        int 10h

        ret
end main