External functions

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You can call external functions that are in a DLL from the PLC-program. Doing this you declare a function (no function block) with PLC|New with exactly the same parameters as the external function. Within the function you call the external function with the key word EXTERNAL followed by the name of the DLL and the function name. Example:

EXTERNAL trysimdll control

The capitalization of the function name has to be noted.

The function in the DLL has to follow the C-call-conventions, that means if you have written the DLL in pascal you will have to set the key word cdecl after the specification of the parameter. Bool, Byte, Char, Int(16-bit), Word(16-bit), DInt (32-bit), Dword(32-bit) and REAL(4 bytes) are only permitted as parameter types.

Please note that the naming of the data types in STEP®7, C and Pascal is not identical:

STEP7	C	Pascal
bool	bool	boolean
char	char	char
byte	byte	byte
word	unsigned short	word
int	short	smallint
dword	unsigned long	dword
dint	long	integer
real	float	single

STEP®7 is a registered trademark of the Siemens AG.