DF-1 Communications & Wiring

Hello. I have some old scales that are currently communicating DF-1 Full Duplex to a board-level device. I'm looking to replace the board level device with a ControlLogix. I may not be creating my messages correctly, but I'm 90% sure I am. I've been evesdropping on the existing setup in order to create the correct messages when I rip out th eold board level device. I'm getting Negative Acknowledgements from the scales when I send my response and Acknowledgement.

I've become confused today as I started reading AB Document 1770-rm516, DF-1 Protocol and Command Set. It shows 4 comm paths, 2 Tx and 2 Rx for Full Duplex. The existing connection on the machine are 3 wire, Rx, Tx and GND. I'm using a 3rd party device for the serial communications and am comfortable with its functionality. I've written my own DF-1 driver within my processor.

Does a DF-1 Full Duplex link use 5 wires, Tx1, Tx2, Rx1, Rx2 and GND? Has anyone wired up and written their own DF-1 Driver in ControlLogix?

Thank you for any help.

I'm a little confused about the role of the devices you describe.

Please try to explain more clearly what the "scales" and the "board level device" are, and what the "third party device" and the "processor" you are writing a DF1 driver in.

Are the "scales" initiating the DF1 messages, or is this "board level device" initiating them ? Which device do you plan to replace with a ControlLogix ?

DF1 protocol is independent of the physical wiring. You can run DF1 over all kinds of physical links, but the most common is RS-232. Basic RS-232 has a Transmit pin, a Receive pin, and a Common pin.

Anything you see with two Rx and two Tx is probably a "4-wire RS-485" implementation. This is far less common than "2-wire RS-485" or RS-232, but it is sometimes used for full-duplex serial communication over long distances.

Thank you for the quick reply. A little more detail:

There is currently some trangle brand Scales filling bags. Each time a bag is filled the scales send out the weight and fill level of the bag via DF-1 over RS-232. The board level device receives this info and may send parameter adjustments to the scales based on the weight history. I am using an rtaautomation NBA which has 2 RS-232 comm ports and populates a ControLogix tag via Ethernet. I've used the NBA to successfully replace a similar system on 2 other packing lines, they talked simple ascii, they are working fine. The 3rd one I've been asked to do is this DF-1 machine. I looking to talk directly to the scales and become the board level dvice, using ControlLogix.

I'm currently testing my logic to replace the Fill Controller (board level device). When I send my DF-1 Message I receive a Negative Acknowledgement from the scales. While reading the previously mentioned AB DF-1 Document the Full Duplex section (Chapter 4 if you want to look) shows 4 communication paths and I'm confused by it. I have 2 comm wires and have never seen an RS-232 comm cable with 4 comm lines.

I won't get a chance to play around more until the weekend and am trying to understand as much as I can before that. Just looking for some clarification that my 3-Wire RS-232 is acceptable for Full-Duplex DF-1.

Thank you.