Communication
11.2 Communication via Modbus
SIWAREX WP231
154 Manual, 07/2014, A5E31238908A-02
The following baud rates can be set:
● 9 600 bit/s
● 19 200 bit/s (default setting)
● 38 400 bit/s
● 57 600 bit/s
● 115 000 bit/s
Functions which can be used by the master are listed below. The structure and contents of
the registers are shown in chapter "Scale parameters and functions (Page 63)".
Read Holding Registers 03 Read one or more 16-bit parameter registers
Write Single Register 06 Write a single parameter register
Write Multiple Registers 16 Write multiple registers
If a request of the master is answered by the SIWAREX module (slave), the SIWAREX
module sends a response frame with or without errors. In the case of a response without
error message, the response frame contains the received function code; in the case of
errors, the highest bit of the function code is set. This corresponds to the Modbus standard.
Afterwards, the master requests the data record DR 32 to check which process-related data
or operator errors exist.
The register assignment is an image of the data records. The chapter → Scale parameters
and functions (Page 63) describes the data records, variables and functions, including the
register addresses. The data records are always checked as complete data packets for
plausibility. For this reason, you must follow a specific procedure to change individual
parameters.
Corresponding command codes must be sent in order to execute commands and to read
and write data records in the Modbus buffer memories. These are described in more detail in
chapter → Command lists (Page 139). The following tables list the Modbus registers used to
process these commands:
Table 11- 4 Command mailbox 1: Highest priority
CMD1_CODE Code of command to be executed USHORT 910
CMD1_TRIGGER Trigger for starting the command USHORT 911
CMD1_STATUS 0=job running; 1=job finished (1 cycle) USHORT 912
CMD1_QUIT 0=no error; <>0=error code USHORT 913
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