INT 21 - DOS 1+ - GET STDIN STATUS
AH = 0Bh
Return: AL = 00h if no character available
= FFh if character is available
Notes:  ^C/^Break checked, and INT 23 called if pressed
standard input is always the keyboard under DOS 1.x, but may be
redirected under DOS 2+
if the interim console flag is set (see AX=6301h), this function
returns AL=FFh if a partially-formed double-byte character is
available
SeeAlso: AX=4406h

See also: 2106

210B - DOS 1+ - GET STDIN STATUS