I am trying to read registers in a resin dryer (Piovan) communication's board via Modbus with a Micrologix 1100. I know what the register address is but I'm having no luck getting it to communicate with the Micrologix. I am using the 1763-NC01 cable, connected it to the Modbus (RS-485) 2 wire connection, but I'm getting nothing. I am using a MSG instruction reading word 1020 (process temperature) into N30:0. I've tried changing everything I can think of, swapped the Modbus cables around, but nothing. I am looking for any ideas or sample PLC logic to try. I figure it is just something simple that I don't have configured correctly but can't seem to find it.
Thanks for any help...

 

Have you configured channel 0?. You have to configure the driver as "Modbus RTU Master" and control line "No Handshaking (485 Network)".

Good luck

 

Thanks for the quick response. Yes I have configured Channel 0 as "RTU Master" and also "No Handshaking". For now I'm just trying to read register 1020 in the OEM communication board which is supposed to be "Process Temperature". I am using the MSG instruction and reading it to N30:0. I have a serial RS-232 to RS-485 adapter that I am going to try today and see if I can use Kepware and read the register. I also may try a different dryer just in case that communication board isn't working. I'll post what I find out later today.
Thanks for all the help...

 

Something I noticed with the message file, is that if you specify a Modbus Register in the MSG instruction, the TFN data is set to 1 less than this value. I haven't checked what actually comes out in the data stream, but when I set the register address in the MSG instruction to the value I want +1, it works. The TFN is the register I want.

Can't find a good reason for this though...

 

Roger,

Within the RsLogix programming environment, you can view the error code in realtime for each of your message instructions.

Double-click on the message instruction in RsLogix and watch for the error code to be displayed during execution.

I've used the error-code to successfully track down DF1 and EtherNet/IP problems in the past, and it should work for Modbus, too.

 

This could as simple as RS-485 goofiness - the issue of what is "A" verse what is "B"? Even grounding could be an issue.

Try swapping the wires of the RS-485. Use a multi-meter to confirm the voltage difference when the 2 cables are NOT connected is reasonable. I will assume the MicroLogix 1100 is using an isolated, floating supply on the serial port. How does this relate to the resin drier? If the resin dryer assume the RS-485 is chassis/earth grounded (or worse, offset by 20000 ohms or something) you should examine simple electrical issues first.

Use a multi-meter with a 'change' signal - my Flukes have a little "+/-" sign which blinks when voltages change. Although I won't see the 9600 baud voltages change via actual voltage levels they are too short in duration, I will see the blinks any time the Master talks.

Even baud rate, RTU-vs-ASCII, etc could be an issue. Start as low in the system as you can.

 

I am trying to read registers in a resin dryer (Piovan) communication's board via a lantronix converter modbus to TCP/IP with Kepware OPC software.

I don't know what the register address are for sure and I'm having no luck getting it to communicate with the Kepware OPC although i am connected. I have tried setting up the Kepware OPC but need someone elses expertize to show me the correct way to set it up. I previously had it working thru a Graytech server but the company decided to not use Graytech software in the future. I believe that the connection is still valid but don't know how to pull a sample of the registers from the connection to the dryer board.

I am looking for any ideas or samples of the registers and Kepware OPC software setup. I figure it is just something simple that I don't have configured correctly but can't seem to find it.

you can email me directly at mmason [at] plastipak.com

Thanks for any help...