INT 21 - Trusted Access - NB.SYS - GET STATE
        AH = 3Fh
        BX = file handle for device "$$NB$$NB"
        CX = 0002h (size of state)
        DS:DX -> buffer for state record
Return: CF clear if successful
            AX = number of bytes actually read (0 if at EOF before call)
        CF set on error
            AX = error code (05h,06h) (see AH=59h)
Program: Trusted Access is a security and access-control package by Lassen
          Software, Inc.; NB.SYS is a device driver to prevent the user from
          terminating CONFIG.SYS or AUTOEXEC.BAT with Ctrl-Break
SeeAlso: AH=40h"NB.SYS",AX=4101h

Format of state record:
Offset  Size    Description
 00h    BYTE    00h off, 01h on
 01h    BYTE    keys being disabled
                bit 0: Ctrl-Break
                bit 1: SysRq
                bit 2: Ctrl and Alt
                bit 3: Ctrl-Alt-Del
                bit 7: all keys (overrides other bits)

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