Modbus Master Overview - HORNER APG EXL10 OCS User Manual

20.3 Modbus Master Overview

For complete Modbus Master instructions, please refer to the Help file in Cscape.
When acting as a Modbus master, there are two primary mechanisms used by the EXL10 to allow the
user to specify the data to be read/written from/to the slaves.
Modbus Master Function Block—This is 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 Cscape
(serial) – Refer to the Modbus Addressing Section.
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). 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, minimal
address conversion is required. Also, if the slave is another Horner product (i.e. another
OCS), 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.
NOTE: Once configuration has been completed on the Network and Devices level, Modbus data
can be directly read/written from graphics objects in the Cscape 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 Cscape Help file.
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This is the preferred method in most applications.
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