Example: Specifying A Modbus-Rtu Command In Master Mode - HMS Anybus Communicator User Manual

8.3.5 Example: Specifying a Modbus-RTU Command in Master Mode

In the following example, a Modbus-RTU command is created in Master Mode. In Modbus-RTU, a
transaction always feature the following parts:
• Slave Address (1 byte)
• Function Code (1 bytes)
• A data field
• CRC (CRC-16)
Furthermore, each command always consists of a query and a response.
• Example Query
Query
DisplayName Slave Address
Object Type
Value
• Example Response
Response
DisplayName Slave Address
Object Type
Value
By default, the Modbus-RTU-specific frame objects are already in place, and a data object is inserted
between the function code and the CRC. These objects cannot be moved or deleted, however it is pos-
sible to add additional objects between the function code and the CRC as desired.
Name the new command by entering its name in the "Command Name" field, and enter a suitable func-
tion code in the "Command ID"-field. If the command is allowed to be broadcasted, check the "Allow
Broadcasting" checkbox.
Anybus Communicator PROFINET User Manual
1 2
Function
Byte Object Byte Object
[SlaveAddress] ID
The value of this byte The value of this byte
constant will be set constant will be set
using the "SlaveAd- using the "Command
dress" parameter (see ID"-field.
"Node Parameters" on
page 27).
1 2
Function
Byte Object Byte Object
[SlaveAddress] ID
This value is linked to The value of this byte
the "SlaveAddress" constant will be set
parameter in the using the "Command
parameter window. ID"-field.
3 4
Data Checksum
Data Object Checksum Object
User User
The size and location The checksum type etc
of the data associated can be selected by the
with this object is user. By default, this is
determined by the set to match the Mod-
user. bus-RTU standard.
3 4
Data Checksum
Data Object Checksum Object
User Depend
The size and location This object will retrieve
of the data associated its settings from the
with this object is corresponding object
determined by the in the Query.
user.
Doc: HMSI-27-309, Rev. 3.11
Commands 45