INT 2F U - ANARKEY.COM v2+ - GET ???
        AX = E301h
Return: DX:BX -> ???

Format of returned data structure for ANARKEY v2.0:
Offset  Size    Description
 -7   7 BYTEs   signature ('ANARKEY')
 00h    WORD    ??? (I see 0001h in v2.0)
 02h    WORD    ??? (I see 0001h in v2.0)
 04h    WORD    ??? (I see 0 in v2.0)
 06h    WORD    PSP segment of next program loaded

Format of returned data structure for ANARKEY v3+:
Offset  Size    Description
 -1     BYTE    multiplex number
 00h    WORD    ??? (I see 0001h in v3.0-4.0)
 02h    WORD    ??? (I see 0001h in v3.0-4.0)
 04h    BYTE    ??? (I see 0 in v3.0-4.0)
 05h    WORD    PSP segment of next program loaded