Need help to build link between RSLogix and MODBUS RTU Master

Shubho · May 8, 2013

I want connect MODBUS RTU device with AB ML1100 PLC to read the holding registers of MODBUS device.

In RSLogix 500 I have already configured the channel for MODBUS RTU Master and in Ladder I hv configured the MSG instruction but till I'm unable to read it. ....plz help.

bernie_carlton · May 8, 2013

Please zip and post your program and a diagram of the wiring connection. Also please provide a link to a manual for the MODBUS device.

Shubho · May 16, 2013

RSLogix 500 - MODBUS RTU

Thank you sir for the replay..

I hv uploaded the .rss file..

kindly find the attachment.

Shubho · May 16, 2013

MODBUS Device details

Here I have used the Multifunction Meter with RS485 port as MODBUS RTU Device.

I hv used RS485 to RS232 converter.. and connect 1st with PC to check MODBUS address & values of
holding registers of Multifunction Meter (the MODBUS RTU Device)using Modscan32 software.

Then I hv connected the converter with RS232 cable of ML1100 PLC

Then I hv configured channel for MODBUS RTU Master

Multifunction Meter details:
Make: Nippen, website: www.[B]nippen[/B]co.com/‎
Model No.: SLM-34

Device ID: 03
Holding registers address: 1001 to 1050
Correspond MODBUS address of Holding registers: 41001 to 41050

pino2003fr · May 16, 2013

how far your ML1100 PLC form meter and did you check the out put off the meter if you're reading something, and may you have to put termination resistors 120 ohms on each end.

bernie_carlton · May 16, 2013

In your communication setup in RSLogix change the "Control Line" as in the attached picture.

Shubho · May 16, 2013

pino2003fr said:
how far your ML1100 PLC form meter and did you check the out put off the meter if you're reading something, and may you have to put termination resistors 120 ohms on each end.

I hv checked meter comm output with PC directly using modscan32.. its ok, but hv not used 12 ohms resistors.

Cable distance between PLC & meter is max 0.5 meter.

ML1100 RS232 cable <-- RS232/485 converter <-- meter

I have attached the connection diagram... kindly find the attachment.

Shubho · May 16, 2013

bernie_carlton said:
In your communication setup in RSLogix change the "Control Line" as in the attached picture.

Sir,
I also hv checked with this option.. but problem remains the same.
I think, my mistake is in comm cable connection. I hv used a RS485 to 232 converter. Converter output side is RS232 female port and in meter side PLC RS232 cable is also female type, so I connect two male RS232 port directly; 2-2, 3-3, 5-5.. like this.. Is it OK?

I hv attach the connection diagram.. kindly find the attachment.

bernie_carlton · May 16, 2013

Why are you using a convertor? The Micrologix 1100 port already has RS485 pins. Refer to the user's manual for the connection.

Shubho · May 16, 2013

Ok sir.. I will try with DH-485 cable.

Is it require to configure the channel in RSLogix or
require to build the DH-485 link in RSLinx ??

bernie_carlton · May 16, 2013

The configuration in RSLogix and downloaded to the PLC is for the PLC < - > Modbus Device communication.

Configuration of RSLinx is for the PLC < - > PC communication.

Shubho · May 16, 2013

ok sir..
thank you so much.

rguimond · May 16, 2013

There is a limitation to the amount of registers you can read or write with each MSG command, too. The exact number escapes me. There are two possible outcomes if the limit is exceeded:

1. The MSG won't work
2. The MSG works, but you only read the number of registers allowed by the constraints of the PLC

Shubho · May 22, 2013

How to use MSG Block?

rguimond said:
There is a limitation to the amount of registers you can read or write with each MSG command, too. The exact number escapes me. There are two possible outcomes if the limit is exceeded:

1. The MSG won't work
2. The MSG works, but you only read the number of registers allowed by the constraints of the PLC

I have connected 1763-NC01 (DH-485) cable with Modbus device to ML1100 and hv configured channel for Modbus master. Here Modbus Device ID = 3

Now what will be the ladder program?
Will I need to use MSG block?
How I will read holding register addr = 1044 at N7:0?

Need help to build link between RSLogix and MODBUS RTU Master

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