Siemens SIMATIC PN/M-Bus LINK - Application Planning; Installation Guidelines

Functions
4.1 Cyclic and acyclic data exchange
PN/M-Bus LINK
Operating Instructions, 03/2018, A5E44260928-AA
17
Acyclic data exchange: Reading measurement data from M-Bus devices
The measured values are transferred from the PN/M-Bus LINK to the S7 control system
through data records. The PN/M-Bus LINK always reads all available measured values from
an M-Bus device and saves the measured values as a data record.
A data record is read via "Read Data Record" (RDREC). The default index number is 600.
A data record contains the user data from the RSP_UD response telegram with the
transmitted measured values, starting with the first DIF. The telegram header is not included
in the data record.
The data block with the measured data contained in the data record is transferred to the
S7 controller without any changes. The corresponding evaluation and further processing of
the measurement data must be performed by the user program.
A data record has the following structure:
Byte
Name
Data type
Value
Description
0 … 1 ResponseCode
UINT16
Device error information
0 No error
1
No data available
2 M-Bus communication error - no data
available
2 … 3 Mode UINT16 Specification of the M-Bus data
structure
0 Variable data structure
CI
1
= 72h/76h
1 Fixed data structure
CI
1
= 73h/77h
4 … 5 Length UINT16 Total length of the M-Bus STRUCT in
bytes
6 … <END> Measured data M-Bus STRUCT Measured data from M-Bus device,
starting with the first DIF (EN1434-3)
1) CI field (control information field) from received RSP_UD response telegram