Hi Yiorgos.

You did not indicate what members this structure consists of.
Let, for example, define it as follows:

typedef struct _STRUCTDEV {
  DWORD iType;
  WORD wPort;
  CHAR strSerialNo[11];
} STRUCTDEV;

An equivalent FoxPro code should be something like this:

#DEFINE SDTYPE_SERIAL 0x0001

DECLARE INTEGER FSL_SelectDevice IN <dll name>;
	STRING @dev, STRING param2

LOCAL cBuffer, nType, nPort, cSerial
nType = SDTYPE_SERIAL
nPort = 1
cSerial = "ABC02000001"

cBuffer = PADR(Chr(nType), 4, Chr(0)) +;
	PADR(Chr(nPort), 2, Chr(0)) +;
	cSerial

nResult = FSL_SelectDevice(@cBuffer, "any string")

If the structure has different definition than you have to make corresponding changes in the way you populate cBuffer.