85
16.3 Modbus Master Overview
For complete Modbus Master instructions
,
please refer to the Help file in i3 configurator.
When acting as a Modbus master, there are two primary mechanisms used by the I3N to allow the user
to specify the data to be read/written from/to the slaves.
Modbus Master Function Block
—For serial only. This is an advanced feature that should only be used in
rare occasions.
Protocol Config
—The Protocol Config is configured in the Hardware Configuration dialog box in i3
configurator (serial and Ethernet). This is the preferred method in most applications.
After the protocol has been selected from the dropdown menu, the
Network
,
Devices
, and
Scan List
become available. The Protocol Config is configured on three different levels:
•
Network
—Parameters, such as the polling rate of the data scan, are specified along with timeout
values, retry, and re-acquisition settings. Serial configuration, baud rate, parity, etc. are also set
here.
•
Devices—
For every slave to be polled, configuration details are added in the Devices dialog box.
This includes Slave ID (serial) and IP Address (Ethernet). Under Device Type, the Modbus
addressing style matching that specified in the slave’s user documentation may be selected. For
instance, some slaves specify Modbus addresses (i.e. 40,001), and others specify offsets (i.e.
0000).
o
Hex or Decimal—
Some specify addresses in hex and others in decimal. By allowing the
user to select the Modbus addressing style for each slave on the network, a minimum of
address conversion is required. Also, if the slave is another IMO product (i.e. another I3N
or an i3), the “Native Addressing” option can be selected (i.e. %R1, %M17, etc.), and this
skips the conversion to Modbus style altogether.
•
Scan List—
This is where the specific Modbus addresses to be read/written from/to each slave are
specified. Up to 32 words of data can be read at the same time.
•
Ethernet Configuration
—Modbus TCP or Modbus UDP is selected here.
NOTE:
Once configuration has been completed on the Network and Devices level, Modbus data can be
directly read/written from graphics objects in the i3 configurator screen editor. This is available even if
the Modbus register is not listed on the scan list.
The above information is just an introduction to the topic. For more detailed information, please consult
the i3 configurator Help file.
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