Communication networks (comm)
[Programmable logic controllers (plc)]

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Detailed Description

Messages are sent from one PLC object to another using PLC code.

The PLC communications object implements message handling between PLC objects.

The following functions are available to send and receive messages.

•  void SNDMSG(char *destination, char *string); 
  

  is used to send a string message to a PLC object.

•  void SNDDAT(char *destination, void *buffer, unsigned int size); 
  

  is used to send a binary message to a PLC object.

•  int RCVMSG(char source[], char buffer[]); 
  

  is used receive a string messages from a PLC object. The buffer must be an array for which sizeof() returns the correct maximum length.

•  int RCVDAT(char source[], void *buffer, unsigned int size); 
  

  is used to receive a binary message from a PLC object.

Each communications networks is defined by a single object that handles all messages between PLC objects linked to it. The network has the following properties

• latency defines the message delivery latency (note this is a functional distribution).
• reliability to define the probability with which a message is delivered at all, and
• bitrate to define the data rate at which messages are delivered (longer messages take longer to be delivered if bitrate is non-zero),

Functions
	comm::comm (MODULE *mod)
	Register the new object class and construct the default object properties.
int	comm::create ()
	Create a new object.
int	comm::init (OBJECT *parent)
	Initialize the new object.
TIMESTAMP	comm::sync (TIMESTAMP t0)
	Synchronize the object.
Variables
static comm *	comm::defaults = NULL
	a pointer to the default values for new objects
static CLASS *	comm::oclass = NULL
	a pointer to the registered object class definition