; more source code at http://www.ahjoe.com/source/srcdown.asp

.286
        public  sendkey, getkey, testkey, buffull, bufempty
code    segment
        assume  cs:code, ds:code

sendkey proc    far
;  ax=charcode
        push    ax
        push    bx
        push    si
        push    di
        push    ds
        cmp     ah, 0
        jnz     sendkj0
        mov     ah, 30h
sendkj0:
        mov     bx, 40h
        mov     ds, bx
        mov     di, ds:[1ch]

        mov     bx, di
        call    incptr
        cmp     bx, ds:[1ah]
        jz      fullk

        mov     ds:[di], ax
        mov     ds:[1ch], bx
fullk:
        pop     ds
        pop     di
        pop     si
        pop     bx
        pop     ax
        retf
sendkey endp                              

getkey  proc    far
; out:
;     ax=key code
; if buf empty, it will wait

        push    bx
        push    si
        push    ds

        mov     ax, 40h
        mov     ds, ax
getkeyrep:
        mov     si, ds:[1ah]
        cmp     si, ds:[1ch]
        jz      getkeyrep
        mov     ax, [si]
        mov     bx, si
        call    incptr
        mov     ds:[1ah], bx
        pop     ds
        pop     si
        pop     bx
        retf	
getkey  endp

testkey proc    far
; out:
;      zf=1  buff empty;
;      zf=0  ax=key code
        push    si
        push    ds

        mov     ax, 40h
        mov     ds, ax
        mov     si, ds:[1ah]
        mov     ax, [si]
        cmp     si, ds:[1ch]

        pop     ds
        pop     si
        retf    
testkey endp


bufempty proc    far    ; test key buffer be empty or not
; out:
;      zf=0  not empty;   zf=1  empty
        push    si
        push    ds

        mov     si, 40h
        mov     ds, si
        mov     si, ds:[1ah]
        cmp     si, ds:[1ch]

        pop     ds
        pop     si
        retf
bufempty endp

buffull  proc    far    ; test key buffer be full or not
; out:
;      zf=0  not full;    zf=1  full
        push    ds
        push    bx
        mov     bx, 40h
        mov     ds, bx
        mov     bx, ds:[1ch]
        call    incptr
        cmp     bx, ds:[1ah]
        pop     bx
        pop     ds
        retf
buffull  endp

incptr  proc    near
        inc     bx
        inc     bx
        cmp     bx, 3eh
        jb      incok
        mov     bx, 1eh
incok:
        retn
incptr  endp

decptr  proc    near
        dec     bx
        dec     bx
        cmp     bx, 1ch
        ja      decok
        mov     bx, 3ch
decok:
        retn
decptr  endp

code    ends
        end     sendkey