Programmable logic controllers (plc)
[Runtime modules]

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Detailed Description

The PLC module can load any DLL that has the following exports.

• _data This is the data structure for variables that must be linked
• _init This is the code that must be called after the DLL is loaded but before _code is called for the first time. This must return the number of seconds before the first call to _code
• _code This is the code that must be called each time to PLC syncs. This must return the number of seconds before the next sync.

The data structure must conform to the following structure:

    struct {
     char *name;
     enum {DT_INTEGER=6, DT_DOUBLE=1} type;
     void *addr;
    } data[];

with the last entry having a NULL name (this is very important).

The compiler will automatically create a conforming DLL from a .plc file having the following typical structure

See Machine Implementation for an example of PLC code

Modules
	Communication networks (comm)
	Messages are sent from one PLC object to another using PLC code.
	Machine implementation
	The machine object implements the PLC code.
Functions
int	plc::create ()
	Create a new object.
EXPORT int	create_plc (OBJECT **obj, OBJECT *parent)
int	plc::init (OBJECT *parent)
	Initialize the new object.
EXPORT int	init_plc (OBJECT *obj)
	plc::plc (MODULE *mod)
	Register the new object class and construct the default object properties.
TIMESTAMP	plc::sync (TIMESTAMP t0, TIMESTAMP t1)
	Synchronize the object.
EXPORT TIMESTAMP	sync_plc (OBJECT *obj, TIMESTAMP t0)
Variables
static plc *	plc::defaults = NULL
	a pointer to the default values for new objects
static CLASS *	plc::oclass = NULL
	a pointer to the registered object class definition

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GridLAB-D^TM Version 1.0

An open-source project initiated by the US Department of Energy