AB Micrologix Modbus RTU?

I'm trying to interface an AB Micrologix 1500 to some Emerson/Control Techniques servo Controllers (FM-3 or FM-4). I'm hoping to be able to communicate over Modbus RTU.

In RSLogix 500, I can configure an MLx 1500 comm channel for Modubus RTU Slave.

I can't determine exactly whether the Emerson/CT controllers are masters of slaves or what but from ancilary information in the documentation I have downloaded I get the feeling that they are slaves.

Does a modbus RTU setup require a master (seems to make sense but I've not spoke modbus ... or Klingon to an AB hack ... before )? Is this possible with the MLx 1500 if required?

Thanks

We have interfaced AB to Emerson drives but this was an SLC 5/04 with a Prosoft Modbus interface card in the rack. The Modbus network needs a Master somewhere because the slaves are waiting for a request to respond to. Maybe there is an adapter card for the Micrologix 1500 rack but I don't know of it. Maybe it will require something more extensive. I think that Control Techniques has FM modules with Devicenet. Maybe that's a way to go.

Modblus RTU is a master / slave protocol. One unit in the network must be the master and initiate all communications transactions. The slaves only speak when spoken to. The ML-1500, to the best of my knowledge, is a slave only.

If you are stuck with all slave hardware in your network, you may be able to link teh units together with some kind of communications bridge. One technique that would work, but may be pricey, is to use two EXOR operator interfaces (http://www.exor-rd.com/). Each EXOR can be teh master on its own network, and they can use the EXOR Uninet to communicate with each other. Contact Didier Sos at EXOR tech support for help in setting this up.

bernie_carlton wrote:

I think that Control Techniques has FM modules with Devicenet. Maybe that's a way to go.

Click to expand...

We looked at that but since we haven't used Devicenet before there is a pretty steep entry price. about $1k for RSNetworx for DNet and then a PIC type box for around $700 or PCMCIA for around $850 and all before I have laid one inch of cable

I like Mr. Remington's business model: "Give away the handles and sell the blades"

Datalink Technologies makes a DH485 to Modbus RTU gateway where the gateway can serve as the Modbus master. I think the model number is DL3500-DH-485 with a list price of $1250. Then you could set your serial port up for DH485 comms and use the MSG instruction to send/receive data to your drives.

Remington's continuing campaign against razor blades notwithstanding.

The MicroLogix 1500 can do DF1 Half-Duplex Master, but not Modbus RTU Master. You're going to need some kind of DF1 or DH485 to Modbus RTU Master translator.

I had a customer recently attach a PanelView 600 with Modbus RTU Master directly to an Emerson motion controller, but that was with no PLC involved.

I know the new A-B small PowerFlex4 AC drives use a protocol called "DSI", which is mostly a superset of Modbus RTU protocol. I wonder if their DF1/DSI converter box has enough documentation to make it useful for anything but DriveTools software.

Probably the DataLink or Prosoft devices are your most straightforward way of going about this.