Int 21H, AH=06H

1 and higher

DIRECT CONSOLE OUTPUT/INPUT

DosWrite DosRead

AH = 06h
DL = output character (except FFh)
DL = FFh - input character

On output:

AL = character output (despite official docs which state nothing is returned) (at least DOS 2.1-7.0)

On input:

ZF set if no character available
          AL = 00h

ZF clear if character available
          AL = character read

does not check ^C/^Break

writes to standard output, which is always the screen under DOS 1.x, but may be redirected under DOS 2+

if the returned character is 00h, the user pressed a key with an extended keycode, which will be returned by the next call of this function

this function reads from standard input, which is always the keyboard under DOS 1.x, but may be redirected under DOS 2+

although the return of AL=00h when no characters are available is not documented, some programs rely on this behavior

AH=02h,AH=09h,AH=0BH

Text based on Ralf Brown Interrupt List Release 61