Modbus RTU with a MicroLogix?

Has anybody ever used the Modbus RTU master driver for channel 0 on a MicroLogix 1200 or 1500?


I would like to use it to pull some status information out of an ABB ACS800 variable speed drive. Looks like I would have to buy the Modbus communications adapter for the drive (RMBA-01) and also an RS-232 to RS-485 converter to go between the drive and the PLC.


Has anybody ever done something like this? Any pitfalls I need to watch for? I’ve never messed with Modbus before…


Is there a less expensive option to get the status information from the drive into my Allen-Bradley PLC?

Aaron

The Data Station Plus could be used in this application. It can convert from Modbus to DF1 or DH485. If you want an HMI you could use a G3, which can provide both the HMI and protocol converter.


Regards,

I have done it with the new MicroLogix1100. I am using 3 of them right now as cheap Ethernet to ModbusRTU translators.

I am running mine as Master devices. I did configure one as a slave when I was testing and that worked well too. The data mapping into the Micrologix data tables was super easy. WAAAAAAAAAAAY easier than the ProSoft cards I have used before.

Easy to configure and works well. No real complaints at all.

RSL

RSL, thanks for the info. I didn't mention the other half of the application. It is to use two of the Prosoft cards in my MicroLogix 1500 to the echo the status info obtained from the drive back to the customer's DCS and also to their SCADA. I think the whole thing is a bit excessive as the customer wants two independent channels to both the SCADA and DCS, but there is still just a single path of communicaions between the VSD and PLC. Again, it is just status info as all the control signal are hardwired.

Dan, is this something your products can do?
To recap:
1 channel of Modbus RTU master communications to the drive.
2 channels of Modbus RTU slave communications to the DCS.
2 channels of Modbus RTU slave communications to the SCADA.

I have no need for an HMI.

At this time, we cannot support that many channels. The DSP only has 3 serial ports, 1 RS485 and 2 RS232 ports. We will be releasing (sometime next year) an expansion card with an additional 232 and 485 port, but they are multiplexed so only one can be used as a slave.

The DSP does have an Ethernet port, so if the SCADA systems support Modbus TCP, they could both communicate to it that way.

Regards,

The spec says comms to the DCS and SCADA will be RS485. No Modbus TCP.

RSL said:

I have done it with the new MicroLogix1100. I am using 3 of them right now as cheap Ethernet to ModbusRTU translators.

I am running mine as Master devices. I did configure one as a slave when I was testing and that worked well too. The data mapping into the Micrologix data tables was super easy. WAAAAAAAAAAAY easier than the ProSoft cards I have used before.

Easy to configure and works well. No real complaints at all.

RSL

Click to expand...

Wow RSL that's a great idea. Thanks!

$

RSL said:

I have done it with the new MicroLogix1100. I am using 3 of them right now as cheap Ethernet to ModbusRTU translators.

I am running mine as Master devices. I did configure one as a slave when I was testing and that worked well too. The data mapping into the Micrologix data tables was super easy. WAAAAAAAAAAAY easier than the ProSoft cards I have used before.

Easy to configure and works well. No real complaints at all.

RSL

Click to expand...

Could you explain exactly how to do this? I need to set up the MicroLogix1100 as a Modbus slave with open access to the I/O and data storage registers.
Thanks