Int 7F Fn 21  - Alloy Ntnx, Mw386 - Send Message Or Command To User(s)     [N]

   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

See Also: AH=22h

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