汇编语言编写DOS下的内存驻留程序(5)

核心提示：current dw 0KeyTab db 59dw dir_cmddb 60dw dir_widedb 61dw dir_asmdb 62dw dir_comdb 63dw dir_exedb 50dw make_macrodb 0 ;This must be last in key tabledir_cmp db

current dw 0
KeyTab db 59
dw dir_cmd
db 60
dw dir_wide
db 61
dw dir_asm
db 62
dw dir_com
db 63
dw dir_exe
db 50
dw make_macro
db 0 ;This must be last in key table
dir_cmp db 'DIR',0dh,0
dir_wide db 'DIR/W',0dh,0
dir_asm db 'DIR *.ASM',0dh,0
dir_com db 'DIR *.COM',0dh,0
dir_exe db 'DIR *.EXE',0dh,0
make_macro db 'MASM MACRO;',0dh,0
db 'LINK MACRO;',0dh,0
db 'EXE2BIN MACRO.EXE MACRO.COM',0dh,0
New_Keyboard_IO proc far
sti
cmp ah,0 ;Is this call a read request?
je ksRead
cmp ah,1 ;Is it a status request?
je ksStat ;Let original routine
jmp Old_Keyboard_IO ;handle remianing subfunction
ksRead:
call KeyRead ;Get next character to return
iret
ksStat:
call KeyStat ;Return appropriate status
ret 2 ;Important!!!
New_Keyboard_IO endp
KeyStat proc near
cmp cs:current,0
jne FakeStat
pushf ;Let original routine
call Old_Keyboard_IO ;Determine keyboard
ret
FakeStat:
mov bx,1 ;Fake a "Character ready" by clearing ZF
cmp bx,0
ret
KeyStat endp
;Read a character from the keyboard input queue,
;if not expanding or the expansion string.
;if expansion is in progress
KeyRead proc
cmp cs:current,0
jne ExpandChar
ReadChar:
mov cs:current,0 ;Slightly peculiar
pushf ;Let original routine
call Old_Keyboard_IO ;Get keyboard status
cmp al,0
je Extended
ReadDone:
ret
Expanded:
cmp ah,59 ;Is this character to expand?
jne ReadDone ;If not,then return it normally
;If so,then start expanding
mov cs:current,offset string
ExpandChar:
push si
mov si,cs:current
mov al,cs:[si]
inc cs:current
pop si
cmp al,0 ;Is this end of string?
je ReadChar ;If so,then read a real char?
ret
KeyRead endp
Initialize:
assume cs:cseg,ds:cseg
mov bx,cs
mov ds,bx
mov al,16h
mov ah,35h
int 21h
mov word ptr Old_Keyboard_IO,bx
mov word ptr Old_Keyboard_IO,es
mov dx,offset New_Keyboard_IO
mov al,16h
mov ah,25h
int 21h
mov dx,offset Initialize
int 27h
cseg ends
end Start