SCADAPack E Modbus Master Operation

There are 2 methods to configure the SCADAPack E rPAC/RTU to be used as a Modbus master. It can be done via IEC-61131-3 programs running on the controller, or it can be accomplished using the Modbus Scanner configuration in SCADAPack E Configurator. The method that you choose to implement depends on where the data you collect from the Modbus slave is required

IEC 61131-3 Programs

Within IEC programs, there are an additional 2 methods. The legacy version uses the I/O devices to poll Modbus slave registers. A second method using Modbus set-up blocks was introduced in firmware 8.12.1. Both of these methods will return Modbus slave data into the IEC 61131-3 program variables. The data can be used in the programs for calculations and then applied to database points (using output I/O devices) if needed.

This method is useful if the Modbus slave data will be manipulated by an IEC 61131-3 program.

Modbus Scanner

A Modbus Scanner feature was also introduced in firmware 8.12.1. This lets a user configure Modbus polling within the SCADAPack E Configurator. Modbus slave data is returned directly into the SCADAPack E point database. If some of the data is needed in a IEC-61131-2 program data can be mapped to program variables using input I/O devices.

This method is useful if the SCADAPack needs to act as a protocol converter between Modbus and DNP3 and/or the majority of the data will be sent to an upstream device as Modbus or DNP3.

Conclusion

Both methods can allow Modbus data to be used in IEC-61131-3 or converted to DNP3 points, the primary function of where the data will be used should be considered when choosing one of the 2 options.

Detailed operation of both methods is described in the SCADAPack E Documentation set (Included with the installation of SCADAPack E Utilities)

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