如果DI>32767,VGA输出不显示

我有一个16位汇编程序(NASM),它切换到VGA图形模式,并试图用纯色填充整个屏幕,但我最多只能填充32767(0x7fff)像素(而不是64000(0xfa00)像素的完整320x200显示器),如果再多,所有白色像素都会因某种原因消失。我假设这是某种有符号的增量,但我不太确定,因为我还在学习。否则,像素可能会出现并被绘制到屏幕上(我使用QEMU)

init.asm:

org 0h
bits 16

%define ENDL 0dh, 0ah

jmp _entry

_entry:
    push msg_hello
    call puts

    jmp entry
entry:
    call toggle_vga
    
    push 0fh
    push 07fffh
    call fill_screen
    
    jmp endp

toggle_vga:
    push ax
    mov ah, 0fh
    mov al, 0h
    int 10h

    cmp al, 13h
    je .toggle_vga_off
    jne .toggle_vga_on
.toggle_vga_on:
    mov ah, 00h
    mov al, 13h
    int 10h
    jmp .toggle_vga_end
.toggle_vga_off:
    mov ah, 00h
    mov al, 03h
    int 10h
    jmp .toggle_vga_end
.toggle_vga_end:
    pop ax
    ret
    
fill_screen:
    push bp
    mov bp, sp
    
    push es
    push ax
    push dx
    push cx
    push di
    
    mov ax, 0a000h
    mov es, ax
    mov dl, [bp + 6]
    mov cx, [bp + 4]
    mov di, 0
.fill_screen_loop:
    cmp di, cx
    jge .fill_screen_done
    
    mov [es:di], dx
    inc di
    
    jmp .fill_screen_loop
.fill_screen_done:
    pop di
    pop cx
    pop dx
    pop ax
    pop es

    pop bp
    ret

puts:
    push bp
    mov bp, sp

    push bx
    push ax
    mov bx, [bp + 4]
.puts_loop:
    cmp byte [bx], 0
    je .puts_done

    mov ah, 0eh
    mov al, [bx]
    int 10h

    inc bx
    jmp .puts_loop
.puts_done:
    pop ax
    pop bx
    pop bp
    ret

endp:
    cli
    hlt

msg_hello: db 'init: loaded successfully.', ENDL, 0