Micro OCS Communications
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 Micro OCS controller 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. 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 avail-
able. The Protocol Config is configured on three different levels:
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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.
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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).
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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 alto-
gether.
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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.
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