The BACnetReader actor reads an xml configuration file to determine what data it needs to read from BACnet devices. This configuration file specifies the BACnet object types and their child elements, ^[2] which can be other BACnet object types or BACnet property identifiers . The xml configuration file has the following syntax: It starts and ends with

<?xml version="1.0" encoding="utf-8"?>
<BACnet>
   <!-- Child elements are not shown. -->
</BACnet>

The above element BACnet requires at least one child element of the form

<Object Type="Device" Instance="123">
   <!-- Child elements are not shown. -->
</Object>

i.e., the element name is Object, the attribute Type needs to be Device and the attribute Instance needs to be set to its instance number, which is a unique number that is assigned at the discretion of the control provider. Any Object element can contain other Object elements and other PropertyIdentifier elements.

The Object elements can have any of the following values for the attribute Type (the meaning of these types is explained in Chapter 12 of the BACnet Standard [ASHRAE 2004] ): Analog Input, Analog Output, Analog Value, Binary Input, Binary Output, Binary Value, Calendar, Command, Device, Event Enrollment, File, Group, Loop, Multi State Input, Multi State Output, Notification Class, Program, Schedule, Averaging, Multi State Value, Trend Log, Life Safety Point, Life Safety Zone, Accumulator, Pulse Converter, Event Log, Global Group, Trend Log Multiple, Load Control, Structured View, Access Door, Lighting Output, Access Credential, Access Point, Access Rights, Access User, Access Zone, Authentication Factor Input, Max ASHRAE, Load Control, Structured View, Access Door, Lighting Output, Access Credential, Access Point, Access Rights, Access User, Access Zone, Authentication Factor Input, Max ASHRAE.

Each of these object types has its own set of properties that can be read or written to. These properties are declared in the element PropertyIdentifier which has one attribute called Name. For example, for the object with type Analog Output, the BACnet standard lists in Table 12-3 the properties shown in Table 5.4, “Properties of the Analog Output Object Type according to BACnet Standard, Table 12-3 (not all properties are shown).” .

Thus, we can set, for example,

<?xml version="1.0" encoding="utf-8"?>
<BACnet>
  <Object Type="Device" Instance="123">
    <Object Type="Analog Output" Instance="1">
      <PropertyIdentifier Name="Present_Value"/>
    </Object>
  </Object>
</BACnet>

which would cause the BACnetReader to read the present value of the BACnet Analog Output object type with instance number 1, which is part of a BACnet Device Object with instance number 123.

<?xml version="1.0" encoding="utf-8"?>
<BACnet>
  <Object Type="Device" Instance="637501">                 
    
    <PropertyIdentifier Name="Local_Date"/>                
    
    <Object Type="Analog Input" Instance="1">              
      <PropertyIdentifier Name="Object_Identifier"/>       
      <PropertyIdentifier Name="Units"/>                   
      <PropertyIdentifier Name="Present_Value"/>           
    </Object>
    
    <Object Type="Analog Output" Instance="2">             
      <PropertyIdentifier Name="Present_Value"
                          Index="2"/>                      
    </Object>
    
  </Object>
  
  <Object Type="Device" Instance="637502">                 
    
    <Object Type="Analog Input" Instance="1">
      <PropertyIdentifier Name="Present_Value"/>
    </Object>
    
    <Object Name="Analog Output" Instance="3">
      <PropertyIdentifier Name="Present_Value"/>
    </Object>
    
  </Object>
</BACnet>

<Object Type="Device" Instance="123">
   <!-- Child elements are not shown. -->
</Object>

The BCVTB contains an actor called BACnetWriter that can write to BACnet devices. The BACnet standard [ASHRAE 2004] defines the conformance codes shown in Table 5.5, “BACnet Conformance Codes.” . The BACnetReader can write to any BACnet properties with the conformance code W.

The BACnetWriter provides the WriteProperty Service that is specified in Section 15.9 in the BACnet Standard [ASHRAE 2004] . The configuration file that is used by the BACnetWriter is identical to the one used for the BACnetReader explained in Section 5.12.2, “Reading from BACnet” , except that the xml elements of type PropertyIdentifier have the additional attributes ApplicationTag, Priority, and Index. These attributes are explained in Table 5.6, “Attributes of the PropertyIdentifier xml element if used to write to a BACnet device.” . The following program listing shows an example configuration file.

<?xml version="1.0" encoding="utf-8"?>
<BACnet>
  <!-- Top level BACnet device -->  
  <Object Type="Device" Instance="637501">

    <!-- BACnet object for analog input -->    
    <Object Type="Analog Input" Instance="1">
      <PropertyIdentifier Name="Present_Value" ApplicationTag="Real" 
			  Priority="15" Index="-1"/>
    </Object>
  </Object>
  <!-- Top level BACnet device -->    
  <Object Type="Device" Instance="637502">
    
    <Object Type="Analog Input" Instance="1">
      <PropertyIdentifier Name="Present_Value" ApplicationTag="Real" 
			  Priority="15" Index="-1"/>
    </Object>
    <!-- BACnet object for analog input -->        
    <Object Type="Analog Input" Instance="2">
      <PropertyIdentifier Name="Present_Value" ApplicationTag="Real" 
			  Priority="15" Index="-1"/>
    </Object>
  </Object>
</BACnet>

For the BACnetWriter, the xml element PropertyIdentifier has the attributes shown in Table 5.6, “Attributes of the PropertyIdentifier xml element if used to write to a BACnet device.” .

Figure 5.43.  Ptolemy II system model that uses the BACnetReader actor.

Figure 5.43 shows a Ptolemy II system model that uses the BACnetReader actor. To configure the BACnetReader, double-click on its icon and add the name of its configuration file that has been developed as described in Section 5.12.2, “Reading from BACnet” . There is also a check-box called continueWhenError. If activated and an error occurs, then Ptolemy II will continue the simulation and the actor will output at its ports the last known value and the error message, unless the error occurs in the first step, in which case the simulation stops. If deactivated and an error occurs, then the simulation will stop, the error message will be displayed on the screen and the user is required to confirm the error message by clicking on its OK button. Thus, select this box if the BCVTB should continue its operation when a run-time error, such as a network timeout, occurs.

The BACnetReader has one input port, which is a trigger port. If the SDF Director is used in the Ptolemy II system model, then this port need not be connected. The BACnetReader has the output ports shown in Table 5.7, “Output ports of the BACnetReader actor.”.

Figure 5.44.  Ptolemy II system model that uses the BACnetWriter actor.

The configuration of the BACnetWriter actor is similar to the configuration of BACnetReader. Figure 5.44 shows a Ptolemy II system model that uses the BACnetWriter. To configure the BACnetWriter, double-click on its icon and add the name of its configuration file that has been developed as described in Section 5.12.3, “Writing to BACnet” . There is also a check-box called continueWhenError. If activated and an error occurs, then Ptolemy II will continue the simulation and the actor will output the error message at its ports, unless the error occurs in the first step, in which case the simulation stops. If deactivated and an error occurs, then the simulation will stop, the error message will be displayed on the screen and the user is required to confirm the error message by clicking on its OK button. Thus, select this box if the BCVTB should continue its operation when a run-time error, such as a network timeout, occurs.

Input into the actor is an array of values that will be written to the BACnet devices according to the order specified in the xml configuration file. In Ptolemy II, such an array can be composed from scalar inputs by using the actor Actors->Array->ElementsToArray.

The BACnetWriter has one input port. This port is used to collect the data that need to be sent to the BACnet devices. The BACnetWriter has the output ports shown in Table 5.8, “Output ports of the BACnetWriter actor.”.