DeviceNet communication via DNI to PLC-5.

It is possible to exchange status and variables between a combination of Genetix GCM and MC³ controllers and DeviceNet scanners, using a 1761-NET-DNI (DNI) module from Allen-Bradley (A-B). It 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.

The DNI has a DeviceNet interface one side and an Allen-Bradley DF-1 interface on the other. A controller can be connected to the DNI using the existing RS-232 interface on the DNI and the existing RS-232 interface on the MC³ or Genetix GCM controller.

For performance reasons, data exchange takes place in block mode. The read segment of the CIT is transferred to the PLC in one read operation, and a part of the write segment is transferred in one write operation. The positioning and content of the data elements in the tables must be tracked all the way from the internal controller's 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 by configuring the DNI, 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 PLC. This is done in with DeviceNet configuration software.

·         Between the scanner tables and the final data tables in the PLC. This is done with PLC programming methods.

This example connects two Merrick  GCM or MC³ controllers to the PLC5/11 Series E Rev B. Controller data will be available in a data tables N10 (Incoming Data), N11 (Outgoing data) and F8 (All floating Point data). Here is a detailed map, that illustrates the relation between the the CITs and the data tables. The Devicenet Scanner Module Installation Instructions from Allen-Bradley is helpful.

This solution is fully supported by Merrick, meaning that we have equipment on hand to furnish tested configurations.

Ladder file for RSLogix5 V6.20. All rungs in Ladder file 2. Data tables used: F8, BT9, N10, N11.

RSNetworx configuration file (V 10.01.00) for two DNI's (Nodes 3 and 4) and one 1771-SDN scanner (Node 0). There is a 1756-DNB scanner in the configuration. It was used as an access method only.

DNI utility configuration files for DNI 1 (Node 3) and DNI 2 (Node 4). The DNI utility is an alternate way to configure the DNI using the Serial Port rather than RSNetworks.

 

The DF-1 Specification is useful for troubleshooting.

This Babbage site is useful to resolve IEEE floating point problems.


2014-05-16/Lars