Cyclic Versus Acyclic Data; Cyclic Data - Siemens SITRANS LR460 Operating Instructions Manual

Communications via PROFIBUS PA
D.3 Cyclic versus acyclic data
Configuring PROFIBUS PA with an S7-300/400 PLC
1. If SITRANS LR460 is not listed in the STEP 7 device catalog, you can download the GSD file
from our website and install it in STEP 7. Go to: Product page (www.siemens.com/lr460) and
click Downloads.
2. Add the SITRANS LR460 "rack": click and drag the SITRANS LR460 folder from the hardware
catalog.
3. Fill the rack with desired modules, by dragging and dropping them from the hardware
catalog.
4. After configuring PROFIBUS PA in steps 2 and 3, download it to the PLC.
5. Add code to the PLC program to read data consistently using the SFC14.
D.3

Cyclic versus acyclic data

When you request data from a device via PROFIBUS PA, you have two choices. Cyclic data is
provided at every bus scan: acyclic data is requested and provided as needed.
Input information is always requested at every bus scan and is set up as cyclic data.
Configuration information is only needed periodically and is set up as acyclic data.
D.4

Cyclic data

When you configure the device on the PROFIBUS PA bus, there are two slots available for
modules.
Note
Each of the slots has to have a module defined in it.
Slot 0 always transmits AIFB1 information; slot 1 defaults to Free Place, but can be changed
to AIFB2 information. If you do not wish to have data transmitted, then you must use a Free
Place module in that slot.
Each of the two Analog Input Function Blocks can be set up to return Level, Distance, or
Volume. Within the function blocks, the values are scaled according to the user requirements
[see Analog Input Function Blocks 1 and 2 (Page 164) for details].
AIFB1 and AIFB2 return 5 bytes of data each:
AIFB1
AIFB2
148
Floating Point
byte 1 byte 2
byte 6 byte 7
byte 3 byte 4
byte 8 byte 9
Operating Instructions, 10/2021, A5E42035355-AB
Status
byte 5
byte 10
SITRANS LR460