Checking for collision of snake with border in 8088 assembly language

Question

org 0x100
jmp start
checkBorder:
    push bp
    mov bp,sp
    push ax
    push bx
    push cx
    push dx
    
    mov ax,[bp+6]
    mov bx,[bp+4]
    cmp ax,17
    jz over
    cmp ax,54
    jz over
    cmp bx,2
    jz over
    cmp bx,23
    jz over
    jmp nover
    over:
        mov ax,0xb800
        mov es,ax
        mov di,1974
        mov si,gover
        mov cx,[glen]
        mov ah,0x70
        cld
            next:
                lodsb
                stosw
                loop next
    mov  ah, 0              ; service 0 – get keystroke 
    int  0x16               ; call BIOS keyboard service 
    nover:
        pop dx
        pop cx
        pop bx
        pop ax
        pop bp
        ret 4
start:
    call clrscr
    mov bx,20
    mov dx,10
    mov [direction],0
    mov word[snake_location],
    l3:
        mov ax,0
        push ax
        call printScore
        mov ax,3
        push ax
        call printLives
        call printRec
        mov  ax, bx
        push ax                ; push x position
        mov  ax, dx
        push ax                ; push y position
        push word [length]     ; push message length
        push word[direction]
        call printSnake        ; call the printstr subroutine
        call delay
        call delay
        call delay
        call clrscr             ; clear the screen 
        push bx
        push dx
        call checkBorder
        mov ah,0x01
        int 0x16
        jz skip
        mov ah, 0
        int 0x16
        cmp al,0x77
        jz u
        cmp al,0x73
        jz d
        cmp al,0x61
        jz l
        cmp al,0x64
        jz r
        cmp al,0x1B
        jz ex
        skip:
            cmp al,0x71
            jnz l3
        
        u:
            sub dx,1
            mov [direction],2
            mov [snake_location]
            jmp l3
        d:
            add dx,1
            mov [direction],3
            jmp l3
        l:
            sub bx,1
            mov [direction],1
            jmp l3
        r:
            add bx,1
            mov [direction],0
            jmp l3
    ex:
    mov ax, 0x4c00
    int 0x21
length: dw 4
score: db 'Score: '
live: db 'Lives: '
slen: dw 7
gover: db 'Game Over!'
glen: dw 10
direction: db 0
snake_location:dw 0

Above is the code snippet for snake game in 8088 assembly language. It is not the complete code but includes the subroutine to check border for collision. Now I have no clue how to check for collision. I have tried to hard code but still it isn't efficient. Suggest me a way to check for collision of the snake. the snake has default length 4 with additional '0' character so it looks something like this "****0". The snake is printed from left to right. The collision will always be of '0' character but I don't know its position as snake is moving as keys are pressed so I can't figure out how to check for collision.

I am getting wrong results due to miscalculation of location of snakes head. I would appreciate any suggestions that would make code better. Thank you!