INT 21,3 - Wait for Auxiliary Device Input
AH = 03 on return: AL = character from the auxiliary device - does not supply error returns - waits for character and reads from STDAUX - default DOS AUX parameters are 2400,N,8,1
AH = 03 on return: AL = character from the auxiliary device - does not supply error returns - waits for character and reads from STDAUX - default DOS AUX parameters are 2400,N,8,1