Data Highway Plus communication via DL2000 KFX to PLC-5.

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It is possible to exchange status and variables between MC³ and Genetix GCM controllers and Data Highway Plus (DH+) equipped PLC's, using a DL2000 KFX interface (KFX). 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.

Later versions of Merrick’s MC³ and all Genetix GCM controllers support 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.

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

The KFX has a DH+ interface one side and an Allen-Bradley DF-1 interface on the other. An MC³ or Genetix GCM controller can be connected to the KFX using the existing RS-422 interface on the KFX and the existing RS-422 interface on the controller.

Data tables are transferred between the controllers and the DH+ host PLC. The positioning and content of the data elements in the tables must be tracked all the way from the internal MC³ 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 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, usually using COP instructions.

Control/Status bits and Integer numbers are organized in 16 bit words, and are accessible to ladder logic directly in the MSG local tables, in this example N12 and N13. Parameters are organized as IEEE 32 bit floating point numbers and are accessible in in F14 and F15.

In our test setup, we used an 18 GA four wire shielded cable for the serial connection, with a 5 pin Phoenix connector at the KFX end and a 4 pin Phoenix connector at the MC³ end. Warning! the KFX ships without connectors! You will need Phoenix Type MSTB 2,5/3-ST-5.08 (order # 17 57 02 2) for the DH+ cable and  MSTB 2,5/5-ST-5.08 (order # 17 57 04 8) for the RS-422 cable. Max cable length is 50 ft with this type of cable. For longer distances, use a two twisted pair, individually shielded cable, such as Belden 9368. Add two terminating resistors at  the MC³ end, 120 ohm, between pins 1,  2 (Tx+ and Tx-) and 3, 4 (Rx+ and Rx-). Connect according to the following table:

MC³ 4-pin

GCM 9-pin
Mini Phoenix

KFX Port B'


Pos 1 (Tx+)

Pos 8  (Tx+)

Pin 1 (Rx+)


Pos 2 (Tx-)

Pos 9 (Tx-)

Pin 2 (Rx-)


Pos 3 (Rx+)

Pos 6 (Rx+)

Pin 3 (Tx+)


Pos 4 (Rx-)

Pos 7 (Rx-)

Pin 5 (Tx-)


Not connected

Pos 5

Pin 4 (Shield)



Pin 1 is the leftmost pin, looking at the connector from the cable entry side.

Com2 is the leftmost four pin Phoenix connector on the bottom board of the MC³ controller.


The test set-up used two MC³ 20.20.B controllers connected to a PLC5/11 series E, Revision B PLC, via two DL2000 KFX. The message logic can be found in Ladder file 2. Data from the MC³ is red into N12 and written from N13. Parameters are then copied into F14 and out of F15. The main 'gotcha' is the way elements in the message rung are represented:

·         Size in elements: Decimal words.

·         Data table address: Octal words.

Here are the files from the test setup

·         The DL32-FREE configuration files, one per KFX. DL32-FREE is a configuration program that comes with the KFX, used to set up DH+ and serial communications parameters. In this example, the Station numbers for the KFX's are 12 and 13.

·         RSLoxix5 (V 6.2) RSP file. All MC³ objects in N12, N13, F14 and F15 have symbols to help you identify where to find useful data.

·         The PLC program report, in PDF format.

·         The MSG set up screens. MC³ at 12: Read Write. MC³ at 13: Read Write.

The DF-1 Specification is useful for troubleshooting.

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