Cyclic Versus Acyclic Data; Cyclic Data - Siemens Sitrans Probe LU Instruction Manual

Oxley Creek WWTP Water Reclamation
(Probe LU Manual) Vendor Manual

Cyclic versus Acyclic Data

When you request data from a device via PROFIBUS PA, there are two possible data
transfer methods. 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.

Cyclic Data

When you configure SITRANS Probe LU 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
changed to
use a
Each of the two Analog Input Function Blocks can be set up to return
. Within the function blocks, the values are scaled according to the user
requirements (please see
and
The first 4 bytes are the floating point representation (IEEE) of the variable. The variables
are the outputs of the function block. The 5th byte is the status word, and the list of
possible values is given in the chart below.
The 5 bytes must be read consistently, in a contiguous chunk: they cannot be read byte by
byte, and cannot suffer an interrupt. If you are using an S7-300 / 400, you will need to use
SFC14 DPRD_DAT: Read Consistent Data of a Standard PD Slave.
1.
For more information, please see
Page 24 SITRANS Probe LU (PROFIBUS PA) – INSTRUCTION MANUAL
information
information. If you do not wish to have data transmitted, then you must
module in that slot.
Analog Input Function Blocks 1 and 2
return 5 bytes of data each:
Floating Point
byte 1 byte 2 byte 3
byte 6 byte 7 byte 8
Analog Input Function Blocks 1 and 2
1
. Slot 1 defaults to Free Place, but can be
Status
byte 4 byte 5
byte 9 byte10 byte10
Doc Id: VM11
Active Date: 15/12/2006
, , or
on page 58 for details).
on page 58.
7ML19985JB02