INT 7F - Alloy NTNX, MW386 - SEND MESSAGE OR COMMAND TO USER(S)
        AH = 21h
        AL = sender's user ID
        DS:DX -> control packet (see below)
Note:   messages or commands are ignored if disabled by the destination user

Format of control packet:
Offset  Size    Description
 00h    BYTE    packet type
                00h message
                01h NTNX command
                02h MW386 command
 01h    BYTE    destination user ID or 'A' for all users
 02h 62 BYTEs   ASCIZ message (packet type 00h)
                BIOS keycodes terminated by NUL byte (type 01h) or word (02h)
Note:   a maximum of 16 keycodes will be processed for NTNX and MW386 commands