Thaks for Your answer, I already did it but no luck. Of course I put sc.dll.lib in Project Settings
I receive
"fll_20 error LNK2019: unresolved external symbol "struct SGlobalMemorytag * __fastcall Init_scom(int)" (?Init_scom@@YIPAUSGlobalMemorytag@@H@Z) referenced in function "void __fastcall InitCom(struct ParamBlk *)" (?InitCom@@YIXPAUParamBlk@@@Z)"

as a linker error message.

Here my portion of code:

*** sc_dll.h
typedef struct SGlobalMemorytag
{
....
)SGlobalMemorytag

SGlobalMemorytag* Init_scom(int);
void Close_scom();
void Timer_proc();


*** My main program

#include "sc.dll.h"
#define MAX_CON 20

SGlobalMemorytag* sg



void InitCom(ParamBlk *parm)
{
   long i = p0.ev_long-1;
   sg = Init_scom(i);
   if(sg == NULL)
      _RetLogical(false);   
   else
   {
     for(int i=0;i<MAX_CON;i++)
         sg->installed[i] = 0;						
   _RetLogical(true);
   }
}

TIA