Format of Telebit ACS parameter block:
Offset	Size	Description	)
 00h	BYTE	command (see #03868)
 01h	BYTE	gateway number
 02h	BYTE	reserved
 03h	BYTE	port
 04h 17 BYTEs	auxiliary buffer
 15h	BYTE	session
 16h	WORD	count of bytes passed to API
 18h	DWORD	buffer pointer passed to/from API
 1Ch	WORD	count of bytes passed from API
 1Eh	BYTE	return code (see #03869)