Category: <b>DOS extenders</b>
<br>Flags: Undocumented function, available only in protected mode<p>
<pre><b>INT 21 - Rational Systems DOS/4GW - GET/SET ???</b>

	AH = FFh
	DH = 0Ch
	DL = ??? (00h or 01h)
Return: CF clear if successful
	    AL = previous value of ???
	CF set on error (DL out of range)
	    AX = FFFFh
</pre>