L-INX/L-GATE User Manual
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LOYTEC
LOYTEC electronics GmbH
processes the resulting value. The default for non-commandable BACnet objects (e.g. AI) is
output (%O). This means the logic writes the value, which is read out of the object over the
BACnet network. With this type of variables the BACnet objects are treated as variables of
the IEC61131 program.
When exposing local I/O to BACnet server objects, the BACnet objects represent the I/O
values and the IEC61131 program behaves like a user from the network on those objects.
Typically sensor values are connected to BACnet input objects (e.g. AI). To read the sensor
value the PLC needs an input variable. Since the default data point direction is output, a
separate access data point for the PLC must be created. For doing so, use the
Add/Remove
BACnet properties
option from the context menu of the data point list and create a read data
point for the Present_Value. Figure 79 shows an example, where the PLC uses the input
‘/BAC/AI2.Present_Value_Read’ to get the sensor values from AI2.
Figure 79: PLC with BACnet objects.
BACnet output objects (e.g. AO) are connected to actuator I/Os. On those BACnet objects
the PLC behaves like a user from the network and needs to write and revoke values at certain
priority slots. For writing with a certain priority to a commandable object, a priority write
data point needs to be created (see LINX Configurator User Manual [2], Section BACnet
Configuration, Write and Read with Priority). This data point is configured with a BACnet
write priority in the Configurator and used as an output in the PLC. The example in Figure
79 writes with priority ‘4’ to AO1 over ‘/BAC/AO1_pri4’.
To revoke values in commandable server objects, the
SetValueState
function block must be
used. It is located in the
Loytec_Support/Service
folder. The I/O variable of the controlled
BACnet object is connected to the
Variable
input of the function block. A Boolean signal
needs to be connected to the
Invalid
input. When this input changes to TRUE, the value is
revoked at the respective priority slot. When it remains TRUE in the next cycle the service
function block is idle. Figure 79 shows an example, how to revoke a value in ‘AO1’ at priority
slot ‘4’.
With the out-of-service feature BACnet server objects can be decoupled from the senor and
actuator I/O equipment. When taken out of service, the I/O variables of the PLC are then
decoupled from the network. The input variable Present_Value_Read of an AI no longer
tracks the sensor value but reflects the value set in the AI from a BACnet OWS. This holds
true for all non-commandable BACnet objects. Writing to the priority output variable of an
AO only updates the priority array but no longer drives the actuator. This holds true for all
commandable BACnet objects.
The out-of-service state is reflected in the data point status and can be accessed with the
ValueState
function block. This function block reads the value state and is used in a similar
fashion as the
SetValueState
function block.
8.6.10 Custom Serial Protocols
A logiCAD program can implement simple custom serial protocols using the
SerialComm
function block. The logic program assigns the Baud rate settings for the protocol as well as a
logical
bus number
. This bus number can be selected on the port configuration Web UI in
order to activate the custom serial protocol on that port.
Custom serial protocols with the following communication properties can be supported: