ControlNet communication via DNI and CN2DN to ControlLogix PLC's.

This solution is no longer fully supported. Contact Merrick Technical support!

It is possible to exchange status and variables between MC³ and Genetix GCM controllers and ControlNet scanners, using one 1761-NET-DNI (DNI) module from Allen-Bradley (A-B) per controller and one 1788-CN2DN linking device (CN2DN) between the DeviceNet segment and ControlNet. The network connection replaces both analog and digital I/O. Full Floating Point accuracy is maintained for variables. Up to 10 variables and 80 I/O points can be configured.

See Genetix GCM Configuration and Troubleshooting for DF-1, or MC3 Configuration and Troubleshooting for DF-1 for details.

Later versions of Merrick’s MC³ controllers and all Genetix GCM controllers supports Allen-Bradley (A-B) DF-1 Serial Communications (DF-1) and exposes a standardized Common Interface Table (CIT), compatible with the A-B “Common Interface File” (CIF) specification. PCCC functions 1 (PLC2 Unprotected Read, 485CIF Read), 8 (PLC2 Unprotected Write, 485CIF Write) and 6 (PLC-2 Diagnostic Status) are supported.

The DNI has a DeviceNet interface one side and an Allen-Bradley DF-1 interface on the other. One controller can be connected to the DNI using the existing RS-232 interface on the DNI and the existing RS-232 interface on the controller.

The CN2DN is a DeviceNet scanner with an upstream ControlNet interface.

Data tables are transferred between the controllers and the ControlNet host PLC. The positioning and content of the data elements in the tables must be tracked all the way from the internal register database to the data structures in the PLC. This is done in several steps:

·         Between the controller register database and the Common Interface Table. Some of this mapping is fixed, and some is configurable.

·         Between the CIT and the corresponding tables in the DNI. This is done either via the DNI Serial port or via DeviceNet configuration software.

·         Between the DNI tables tables exposed to DeviceNet and the scanner table in the CN2DN. This is done in with DeviceNet configuration software.

·         Between the scanner table in the CN2DN and the I/O data structures in the ControlLogix PLC. This is done with ControlNet configuration software and with PLC programming methods.

·         Between the I/O data structures in the CN2DN and the final, formatted data structures in the ControlLogix PLC. This is done with PLC programming methods.

Different data types are used for control/status bits, integer numbers and floating-point numbers. Control/Status bits and Integer numbers are organized in 16 bit words, packed into 32 bit DWORDS. Parameters are organized as IEEE 32 bit floating point numbers, each located in one DWORD.

See Genetix GCM Configuration and Troubleshooting for DF-1, or MC3 Configuration and Troubleshooting for DF-1  and DeviceNet communication via DNI to ControlLogix PLC's for details.

Usable downloads:

RSNetworx for DeviceNet configuration file (V 4.12.00) for two DNI's and one CN2DN.

RSNetworx for ControlNet configuration file (V 4.11.00) for one CN2DN and a 1756/A4-A chassis with a 1756-CNB ControlNet scanner.

DNI configuration files for DNI 1 and DNI 2

RSLogix 5000 program (V 15.00.00) for extracting useful data and verify network integrity. In this example, all MC³ data is transferred in and out of an array of a user defined datatype, called MC3. The array has two elements, since there are two MC³ controllers connected. Extraction and insertion take place in the MC3_SCH scheduled programs. You can cut and paste both the data definitions and the ladder logic.

The DF-1 Specification is useful for troubleshooting.

This Queens College site is useful to resolve IEEE floating point problems.


2014-05-08/Lars