GLOBAL-DP-INFO FC 99 - How it works

Hello, Ive been working on a project with s7300 cpu18. In project I found a function, which I can’t understand. The function is protected and the author is Siemens, but is not SFC. Also I could not find it in any stdlib form step 7. This FC is diagnostic for profibus network. Can some one explain how it works ?

FC 99 “Glabal_DP_Info”

CHECK_ACTIV := [in:bool]

EXTERNAL_DP_INTERFACE := [in:bool]

DP_MASTERSYSTEM := [in:int]

DATA_FIELD := [Any pointer]

SUM_SLAVES_NOT_PRESENT := [inout:int]

LIST_SLAVES_NOT_PRESENT := [inout:Any pointer]

SUM_SLAVES_ERROR := [inout:int]

LIST_SLAVES_ERROR := [inout:Any pointer]

RETVAL := [inout:int]

BUSY := [inout:bool]