How to find address for ML 1200 for modbus or RS485

I am unable to get the details for Allen Bradley Micrologix 1200 for modbus using USB to RS485 converter in raspberry Pi how to read data from modbus, i am very new to this thing and i don't know what to do so please help me with this issue.

Do you mean that the docs for the device do not tell you the modbus data structure and registers?

Is this an educational project or something? This bears an amazing similarity to this thread from @Jayeshpitale1. Communication Between RS485 to Node red on raspberry pi

@Colin i don't know about that i am using it for industrial purpose and i am new too this stuff because we don't have an experience person to tell on this thing so i might think i would get a better help in forum rather comparing some one else post to me

You didn't answer this question

We need to know exactly what the problem is. Are you in the same organisation as @Jayeshpitale1? If so then it would be better if just one of you asked questions.

@Colin ther might be similarity between my and his question but i am totally new in this issue as i don't have a proper knowledge about it so please let me know if you can help me with my question also note i don't know who he is. So i need a proper assistance.

Please answer these simple questions.

  1. Do you understand the basics of the modbus protocol?

  2. Does the manual for the device tell you how to access the device with modbus, and what registers to use?

1). I don't know as i am beginner in that.
2). The manual has a modbus address but i don't know which and what to use.

The first thing you must do is to spend a few hours teaching yourself about modbus. That is nothing to do with node red. When you have done that, install node-red-contrib-modbus, look at the help text and try to understand what the nodes do. I suggest starting with the modbus read node and see if you can make it read data from the device.

According to this slide :point_down: the ML 1200 does not support RS485.

Your options appear to be...

  1. connect via RS232 and use ModBus RTU protocol
  2. Add a 1761-NET-ENI and use the CIP EtherNet/IP nodes or PCCC nodes
  3. connect via RS232 and try the DF1 nodes
  4. connect via RS232, read the manual & use Node-RED serial port nodes to read/write ASCII
  1. You can use RS485 to RS232 converter and use Modbus protocol.
  2. You can use 1761-NET-AIC

You set the address in ML 1200

What happened to option 5? :slight_smile:

Not sure it would be worth the hassle purchasing or wiring up 2nd convertor...

...Since it is a PI the OP is using, it would make more sense to either use the built in RS232 or spend ÂŁ8 on a USB to RS232

Sorry. Item 5 is missing:
5. Use the df1 external program created by Stephane Leicht - Not Modbus

If the author of the thread wants to:
a) connect devices over a greater distance
b) connect several devices, then Modbus is used.

Unfortunately, the solution presented in your point 3 requires ST-One hardware

Are you sure? What prevents this node from running on a raspberry PI?

"Missing "@protocols/node-df1" dependency, avaliable only on the ST-One hardware. Please contact us at "" for pricing and more information."
This message shows up when I try to boot with a different USB/RS232 interface.
Tested on PC with Debian 11

1 Like

Any one could help me how to find address about modbus using function node

What do you mean by 'find address'. What address is it that you are looking for? The unit address on modbus, or the register number in the device or what?

I mean that i need the tag N7:10 which has a timer in ML so i need this tag to modbus address for Node red dashboard

I have never used modbus with a Bradley PLC but typically, a non modicon PLC that doesn't use native modbus style addressing uses a mapping.

E.g. I imagine somewhere (in ladder or in some settings) an area of memory is mapped from native PLC address to modbus addresses). Sometimes this is automatic mapping.

Once you know what memory addresses are mapped from PLC address to modbus addresses then you have all the answers.

To find that out you can study the manufacturer's documentation, or contact the manufacturer or their representative, or a forum relevant to the product.