Format of CAPI message:
Offset	Size	Description	)
 00h	WORD	total message length, including header
 02h	WORD	application ID (see AH=01h)
 04h	BYTE	command (see #04072,#04073)
 05h	BYTE	subcommand (see #04072,#04073)
 06h	WORD	message sequence number
		0000h-7FFFh messages from application to CAPI (and replies)
		8000h-FFFFh messages from CAPI to application (and replies)
 08h	var	message data (max 172 bytes for v1.1 only)