INT 21,7 - Direct Console Input Without Echo

AH = 07

on return:

AL = character from STDIN

- waits for keyboard input until keystroke is ready

- character is not echoed to STDOUT

- returns 0 for extended keystroke, then function must be

called again to return scan code

- ignores Ctrl-Break and Ctrl-PrtSc

- see ~INT 21,1~