Functions
4.3 Cyclic data exchange between controller and PN/BACnet LINK
PN/BACnet LINK
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Operating Instructions, 10/2017, A5E39895543-AA
4.3
Cyclic data exchange between controller and PN/BACnet LINK
4.3.1
Data exchange between controller and PN/BACnet LINK
Cyclic data exchange
The cyclic data exchange between S7 controller and the PN/BACnet LINK is performed via
PROFINET IO.
The data to be transferred belong to the IO process image of the S7 controller. This data is
written to the "Present_Value" property of the BACnet objects defined during configuration or
read from there. With a read operation,in addition to the actual value, the status of this value
is also transmitted in the cyclic process image. This status results from the "Status_Flags"
property of the associated object.
With write operations, in addition to the value to be transmitted, its status must also be set by
the S7 program. This status is then transferred to the "Status_Flags" property of the
corresponding BACnet object.
With PROFINET IO, a maximum of 1440 bytes of data (user data and associated data) can
be exchanged in each cycle for each transmission direction.
Data formats
The values of "Binary input" and "Binary output" objects are transferred as bytes in each
case. The actual value of these objects is transmitted in the least significant bit.
The values of "Analog input" and "Analog output" objects are each transferred as float32
values. For 32-bit floating-point values, a format conversion is performed between the format
used in the S7 controller and the format used for the REAL data type in the BACnet network
(endianness correction).
Summary of Contents for SIMATIC PN/BACnet LINK
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