Format of HLLAPI parameter control block:
Offset	Size	Description	)
 00h  3 BYTEs	signature = 'PCB'
 03h	BYTE	function number (see #03873,#03874)
 04h	WORD	segment of control string
 06h	WORD	offset of control string
 08h	WORD	length of control string, unless explicit end-of-str char set
 0Ah	BYTE	unused (IBM)
		ControlString[0] (Rabbit)
 0Bh	WORD	return code (see #03876)
 0Dh	WORD	maximum length of control string (IBM)
		unused (Rabbit)