8086汇编语言初学者教程(第四部分)
中断
中断是一系列功能调用。这些功能调用使得编程更加容易。
比如，你想在打印机上输出一个字符，你只需要简单的调用
中断，它将帮你完成所有的事情。另外还有控制磁盘和其他
硬件工作的中断。我们将这些功能调用称作软件中断。
不同的硬件同样可以触发中断，这些中断称作硬件中断。这里，
我们只介绍软件中断(software interrupts)。
触发一个软件中断，需要使用INT指令，它的使用方式非常简单：
INT value
上面value的取值范围是从 0 到 255 （或者0到0ffh），通常我们
使用十六进制。
你也许猜测只有256个中断调用，但是这是不正确的。因为每一
个中断都有子功能。
在调用一个中断的子功能之前，需要设置AH寄存器。
每一个中断最多可以拥有256个子功能（于是，我们有
256*256＝65536个功能调用）。一般情况下使用AH寄存器，但是
一些情况下可能使用另外的寄存器。通常，其他的寄存器
是用来传递数据和参数的。
下面的例子调用了 INT 10h中断0Eh子功能输出字符串‘Hello!'。
这个功能作用是在屏幕上显示一个字符，然后光标进一，如果
需要还滚屏。
#MAKE_COM# ; 生成com文件的指令
ORG 100h
；我们使用的这个子功能没有返回值，
；所以我们只用设置就可以了。
MOV AH, 0Eh ; 选择子功能
；int 10h/0eh 子功能，输出放在
；AL寄存器中的ASCII码对应的字符
MOV AL, 'H' ; ASCII码: 72
INT 10h ; 输出
MOV AL, 'e' ; ASCII 码: 101
INT 10h ; 输出
MOV AL, 'l' ; ASCII 码: 108
INT 10h ; 输出
MOV AL, 'l' ; ASCII 码: 108
INT 10h ; 输出
MOV AL, 'o' ; ASCII 码: 111
INT 10h ; 输出
MOV AL, '!' ; ASCII 码: 33
INT 10h ; 输出
RET ; 返回操作系统
|
将上述程序拷贝粘贴到Emu8086代码编辑器，点击
[Compile and Emulate] 按钮，运行！
关于中断更多的知识，请查阅下面的英文文档：
Interrupts currently supported by emulator
Quick reference:
A list of supported interrupts with descriptions:
INT 10h / AH = 00h - set video mode.
input:
AL = desired video mode.
These video modes are supported:
00h - Text mode 40x25, 16 colors, 8 pages.
03h - Text mode 80x25, 16 colors, 8 pages.
INT 10h / AH = 01h - set text-mode cursor shape.
input:
CH = cursor start line (bits 0-4) and options (bits 5-7).
CL = bottom cursor line (bits 0-4).
When bits 6-5 of CH are set to 00, the cursor is visible, to hide a cursor set these bits to 01 (this CH value will hide a cursor: 28h - 00101000b). Bit 7 should always be zero.
INT 10h / AH = 02h - set cursor position.
input:
DH = row.
DL = column.
BH = page number (0..7).
INT 10h / AH = 03h - get cursor position and size.
input:
BH = page number.
return:
DH = row.
DL = column.
CH = cursor start line.
CL = cursor bottom line.
INT 10h / AH = 05h - select active video page.
input:
AL = new page number (0..7).
the activated page is displayed.
INT 10h / AH = 06h - scroll up window.
INT 10h / AH = 07h - scroll down window.
input:
AL = number of lines by which to scroll (00h = clear entire window).
BH = attribute used to write blank lines at bottom of window.
CH, CL = row, column of window's upper left corner.
DH, DL = row, column of window's lower right corner.
INT 10h / AH = 08h - read character and attribute at cursor position.
input:
BH = page number.
return:
AH = attribute.
AL = character.
INT 10h / AH = 09h - write character and attribute at cursor position.
input:
AL = character to display.
BH = page number.
BL = attribute.
CX = number of times to write character.
INT 10h / AH = 0Ah - write character only at cursor position.
input:
AL = character to display.
BH = page number.
CX = number of times to write character.
INT 10h / AH = 0Eh - teletype output.
input:
AL = character to write.
This functions displays a character on the screen, advancing the cursor and scrolling the screen as necessary. The printing is always done to current active page.
INT 10h / AH = 13h - write string.
input:
AL = write mode:
bit 0: update cursor after writing;
bit 1: string contains attributes.
BH = page number.
BL = attribute if string contains only characters (bit 1 of AL is zero).
CX = number of characters in string (attributes are not counted).
DL,DH = column, row at which to start writing.
ES:BP points to string to be printed.
INT 10h / AX = 1003h - toggle intensity/blinking.
input:
BL = write mode:
0: enable intensive colors.
1: enable blinking (not supported by emulator!).
BH = 0 (to avoid problems on some adapters).
Bit color table:
Character attribute is 8 bit value, low 4 bits set foreground color, high 4 bits set background color. Background blinking not supported.
HEX BIN COLOR
0 0000 black
1 0001 blue
2 0010 green
3 0011 cyan
4 0100 red
5 0101 magenta
6 0110 brown
7 0111 light gray
8 1000 dark gray
9 1001 light blue
A 1010 light green
B 1011 light cyan
C 1100 light red
D 1101 light magenta
E 1110 yellow
F 1111 white
INT 11h - get BIOS equipment list.
return:
AX = BIOS equipment list word, actually this call returns the contents of the word at 0040h:0010h.
Currently this function can be used to determine the number of installed number of floppy disk drives.Bit fields for BIOS-detected installed hardware: Bit(s) Description 15-14 number of parallel devices. 13 not supported. 12 game port installed. 11-9 number of serial devices. 8 reserved. 7-6 number of floppy disk drives (minus 1): 00 single floppy disk; 01 two floppy disks; 10 three floppy disks; 11 four floppy disks. 5-4 initial video mode: 00 EGA,VGA,PGA, or other with on-board video BIOS; 01 40x25 CGA color; 10 80x25 CGA color (emulator default); 11 80x25 mono text. 3 not supported. 2 not supported. 1 math coprocessor installed. 0 set when booted from floppy (always set by emulator).
INT 12h - get memory size.
return:
AX = kilobytes of contiguous memory starting at absolute address 00000h, this call returns the contents of the word at 0040h:0013h.
Floppy drives are emulated using FLOPPY_0(..3) files.
INT 13h / AH = 00h - reset disk system, (currently this call doesn't do anything).
INT 13h / AH = 02h - read disk sectors into memory.
INT 13h / AH = 03h - write disk sectors.
input:
AL = number of sectors to read/write (must be nonzero)return:
CH = cylinder number (0..79).
CL = sector number (1..18).
DH = head number (0..1).
DL = drive number (0..3 , depends on quantity of FLOPPY_? files).
ES:BX points to data buffer.
CF set on error.Note: each sector has 512 bytes.
CF clear if successful.
AH = status (0 - if successful).
AL = number of sectors transferred.
INT 15h / AH = 86h - BIOS wait function.
input:
CX:DX = interval in microsecondsreturn:
CF clear if successful (wait interval elapsed),
CF set on error or when wait function is already in progress.
Note:the resolution of the wait period is 977 microseconds on many systems, Emu8086 uses 1000 microseconds period.
INT 16h / AH = 00h - get keystroke from keyboard (no echo).
return:
AH = BIOS scan code.
AL = ASCII character.
(if a keystroke is present, it is removed from the keyboard buffer).
INT 16h / AH = 01h - check for keystroke in keyboard buffer.
return:
ZF = 1 if keystroke is not available.
ZF = 0 if keystroke available.
AH = BIOS scan code.
AL = ASCII character.
(if a keystroke is present, it is not removed from the keyboard buffer).
INT 19h - system reboot.
Usually, the BIOS will try to read sector 1, head 0, track 0 from drive A: to 0000h:7C00h. Emulator just stops the execution, to boot from floppy drive select from the menu: 'Virtual Drive' -> 'Boot from Floppy'
INT 1Ah / AH = 00h - get system time.
return:
CX:DX = number of clock ticks since midnight.
AL = midnight counter, advanced each time midnight passes.
Notes:
There are approximately 18.20648 clock ticks per second,
and 1800B0h per 24 hours.
AL is not set by emulator yet!
MS-DOS can not be loaded completely in emulator yet, so I made an emulation for some basic DOS interrupts also:
INT 20h - exit to operating system.
INT 21h / AH=09h - output of a string at DS:DX.
INT 21h / AH=0Ah - input of a string to DS:DX, fist byte is buffer size, second byte is number of chars actually read.
INT 21h / AH=4Ch - exit to operating system.
INT 21h / AH=01h - read character from standard input, with echo, result is stored in AL.
INT 21h / AH=02h - write character to standard output, DL = character to write, after execution AL = DL.
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