Ethernet communication via ENI to SLC5/05 Channel 1.

It is possible to exchange status and variables between one MC³ or Genetix GCM controllers and an Allen-Bradley SLC5/05 PLC using a 1761-NET-ENI Series B or C module (ENI) 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 Common Interface Table (CIT) in the Genetix GCM and the MC³, is transferred to and from the A-B “Common Interface File” (CIF). PCCC functions 1 (PLC2 Unprotected Read, 485CIF Read), and 8 (PLC2 Unprotected Write, 485CIF Write) and 6 (PLC-2 Diagnostic Status) are supported.

For performance reasons, data exchange takes place in block mode. The read segment of the CIT is transferred to the PLC in with one MSG read instruction, and a part of the write segment is transferred in one MSG write instruction. 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 GCM or MC³ register database and the CIT. Some of this mapping is fixed, and some is configurable within the GCM or MC³.

·         Between the CIT and the target data tables in the PLC. This is defined in the MSG instructions.

·         Between the target data tables in the PLC and the final, formatted data tables in the PLC. This is done with PLC programming methods, using COP instructions.

Control/Status bits and Integer numbers are organized in 16 bit words. Parameters are organized as IEEE 32 bit floating point numbers.

The cable between the ENI and the GCM is an Allen-Bradley 1761-CBL-PM02, cut near the DB9 connector. Peel and connect the brown wire to the GCM’s 9 pos Phoenix connector, brown to pos 2, red to pos 3 and green to pos 4. Set the ENI serial port baud rate to 38.4K.

For MC³, use the same cable and add a male – male adapter where pins 2 and 3 are crossed (null modem). Set the ENI serial port baud rate to 19200.


The message logic can be found in Ladder file 2. Note the somewhat confusing message instruction details. Data is red into N10:1 and written from N11:1. Parameters are then copied in and out of F8. The main 'gotcha' is that you have to set the word order to FFF (Monitor page P1:[K] or using the CUI: set Advanced Setup | Communications | GCM Port 2 | Numeric Data | Word Order to 4095.

·         Size in elements: Decimal words.

·         Data table address: Octal words.

Here are the files from the test setup:

·         RSLogix500 (V 8.10) RSS files for Genetix GCM and MC³

·         Here is the ladder listing, in PDF format.

·         The set up screens for the MSG instructions: Read, Read Multihop, Write, Write Multihop.

·         Channel 1 properties set up screen.

The DF-1 Specification is useful for troubleshooting.

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