Communication
11.1 Communication via Modbus
SIWAREX WT241
96 Manual, 05/2015, A5E36046748A
Example
A parameter is to be read from data record 3 (DR 3).
● First, write register CMD3_CODE with 2003 (2000 plus the number of the data record =
read data record).
● Then write CMD3_TRIGGER with "1". The DR3 is then updated in the Modbus buffer
memory.
● It is now possible to read one or more registers with the corresponding variable(s). The
data consistency of the registers read at this time is guaranteed.
You can find all further command numbers in chapter → Command lists (Page 87).
Example
A current measured value is to be read out from DR 30.
⇒ The register can be directly requested because its contents are automatically refreshed in
the SIWAREX module at the specified measuring rate of 100 Hz and are always available
up-to-date.
11.1.6 Writing registers
If you wish to write registers from the data records DR 3 to DR 29, you must first export the
corresponding data record to the internal output buffer using an appropriate command.
Individual registers can then be written. The complete data record must subsequently be
written internally using an appropriate command. A plausibility check of the complete data
record is carried out in the process.
Example
A parameter from DR 3 is to be written.
● First, write register CMD3_CODE with 2003 (2000 plus the number of the data record).
● Then write CMD3_TRIGGER with "1". The DR 3 is then updated in the Modbus memory.
● You can now write or change one or more registers with the corresponding variable. If
you wish to transfer the written/changed registers to the scale, it is necessary to write the
complete data record:
● First, write register CMD3_CODE with 4003 (4000 plus the number of the data record =
write data record).
● Then write CMD3_TRIGGER with "1".
● The data record is then transferred to the process memory in the SIWAREX module. All
registers of the data record are checked for plausibility in the process.
If the plausibility check fails, the complete data record is not written and a message is output
to the user (from the area of data/operator errors).
You can find all further command numbers in chapter → Command lists (Page 87).
In addition, an online document is available for working with SIWAREX WP231 and Modbus
→ Modbus communication of WP231
(http://support.automation.siemens.com/WW/view/de/77913998).
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