16位x86汇编求助：无法设置黄前景蓝背景显示

Hey there! As someone who’s tinkered with 16-bit x86 assembly in DOSBox back in the day, let’s break down what’s likely tripping you up here. Your issue with color not showing up (stuck on white-on-black) usually boils down to a few common missteps with text mode attributes, video mode setup, or how you’re outputting characters. Let’s dive in:

First, Let’s Clarify Text Mode Basics #

In DOS’s standard 80x25 color text mode (mode 0x03), every on-screen character takes up 2 bytes in video memory (0xB8000):

• 1st byte: ASCII character code
• 2nd byte: Attribute byte (high 4 bits = background color, low 4 bits = foreground color)
  • Blue background = 0x10, yellow foreground = 0x0E → combined attribute = 0x1E

Common Issues & Fixes #

1. You might be setting the wrong video mode

If you accidentally switched to a graphics mode (like 0x13 for 320x200 256-color), text output works completely differently (pixel-by-pixel instead of character+attribute). Double-check your video mode setup code:

; Correct: Set 80x25 color text mode
mov ah, 0x00
mov al, 0x03  ; This is the key—0x03 is standard color text
int 0x10

2. Your clear-screen call is using default attributes

When you call the scroll/clear screen interrupt (int 0x10, function 0x06), the BH register defines the fill attribute. If you left BH as 0x07 (white-on-black), it’ll overwrite the entire screen with that color, even if you set attributes later. Fix it like this:

; Clear screen with yellow-on-blue (attribute 0x1E)
mov ah, 0x06
mov al, 0x00  ; 0 = clear entire screen
mov bh, 0x1E  ; Blue background + yellow foreground
mov ch, 0x00  ; Top-left row
mov cl, 0x00  ; Top-left column
mov dh, 0x18  ; Bottom-right row (24, since we start counting at 0)
mov dl, 0x4F  ; Bottom-right column (79)
int 0x10

3. You’re not specifying attributes when outputting characters

If you’re using the teletype output function (int 0x10, function 0x0E), it uses the current attribute at the cursor position. If you didn’t set that attribute first, it’ll default to whatever was left from the clear screen or video mode setup. Instead, use function 0x09 to explicitly set the attribute for your text:

; Set cursor to (10,10) first
mov ah, 0x02
mov bh, 0x00  ; Video page 0
mov dh, 0x0A  ; Row 10 (0-indexed)
mov dl, 0x0A  ; Column 10 (0-indexed)
int 0x10

; Output a 'H' with yellow-on-blue attribute
mov ah, 0x09
mov al, 'H'   ; Character to print
mov bh, 0x00  ; Video page
mov bl, 0x1E  ; Attribute (blue bg + yellow fg)
mov cx, 0x01  ; Number of times to repeat the character
int 0x10

4. Direct video memory writes are missing the attribute byte

If you’re writing directly to 0xB8000, make sure you’re writing 2 bytes (character + attribute), not just the character byte. For example:

; Write 'H' at top-left corner with yellow-on-blue
mov word [0xB8000], 0x1E48  ; 0x1E = attribute, 0x48 = 'H'

If you only write mov byte [0xB8000], 'H', the attribute byte will stay as whatever was there before (probably white-on-black).

Full Working Example #

Here’s a complete NASM .COM program that ties all this together:

org 0x100  ; DOS .COM program entry point

section .text
start:
    ; Set 80x25 color text mode
    mov ah, 0x00
    mov al, 0x03
    int 0x10

    ; Clear screen with yellow-on-blue
    mov ah, 0x06
    mov al, 0x00
    mov bh, 0x1E
    mov ch, 0x00
    mov cl, 0x00
    mov dh, 0x18
    mov dl, 0x4F
    int 0x10

    ; Move cursor to center of screen
    mov ah, 0x02
    mov bh, 0x00
    mov dh, 0x0C  ; Row 12
    mov dl, 0x27  ; Column 39
    int 0x10

    ; Print "Hello, Assembly!" with yellow-on-blue
    mov ah, 0x09
    mov al, 'H'
    mov bh, 0x00
    mov bl, 0x1E
    mov cx, 0x01
    int 0x10
    ; Repeat for each character, or loop through a string—you get the idea

    ; Exit to DOS
    mov ah, 0x4C
    int 0x21

Quick Troubleshooting Checklist #

• Did you confirm you’re using text mode 0x03 (not a graphics mode)?
• Is your clear-screen call setting BH to 0x1E instead of 0x07?
• Are you explicitly specifying the attribute when printing characters (either via int 0x10 function 0x09 or full 2-byte writes to video memory)?

Give these fixes a shot—odds are one of them is the culprit. Let me know if you’re still stuck!

内容的提问来源于stack exchange，提问作者Erin Murphy