DF-1 communication via Micrologix Serial Port.

It is possible to exchange status and variables between one MC³ or Genetix GCM controllers and an Allen-Bradley MicrologixPLC using the standard serial port (Channel 0) on the PLC. It replaces both analog and digital I/O. For 1100 and 1400, Full Floating Point accuracy is maintained for variables. Up to 10 variables and 80 I/O points can be configured. The Micrologix 1000 does not support floating point numbers, but it can be used as a logic add-on and a digital I/O expander.

    

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 CPW instructions.

Control/Status bits and Integer numbers are organized in 16 bit words. Parameters are organized as IEEE 32 bit floating point numbers. The entire CIT read section (R0 – R27) is red into N12:0 – N12:27 with an MSG Read instruction, and the first 8 words of the write section is written from N13: 0 – N13:7 with an MSG Write instruction. The floating point part of the read section is parsed into F14:0 – F14:10 using CPW. The first three members of the floating point part of the write section is then parsed from F15:0 – F15:3.

 

The cable between the Micrologix 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, pos 2, red to pos 3 and green to pos 4. Set Channel 0 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 Channel 0 baud rate to 19200.

 

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

We have a test set-up a Merrick, that we use for support. An MC³ 20.20.B or a Genetix GCM controller is connected to a Micrologix 1400 Series A PLC.

Some examples, first for Micrologix 1100:

·         RSS file from RSLogix500 (V 8.10).

·         Here is the ladder listing, in PDF format.

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

·         Channel 0 properties set up screen.

 

For Micrologix 1400

·         RSS file from RSLogix500 (V 8.10).

·         Here is the ladder listing, in PDF format.

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

·         Channel 0 properties set up screen.

 

RSS file For Micrologix 1000, series E or later, for expanding a GCM or MC³ IO capabilities, and add external logic.

 

The DF-1 Specification is useful for troubleshooting.

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


2014-05-14/Lars