Connecting Allen Bradley Micrologix 1200 to RPi via Rs485

Hi there I am new with this thing and i don't know how to connect Allen Bradley Micrologix 1200 PLC to Raspberry Pi using USB to RS485 in NodeRED i don't know whether the device is communicating with RPi or not i surf the web for this and i got some point about modbus and all i tried to see whether i can use modbus but i don't know which address has to put and how to read data from PLC.

Hi Jayeshpitale! Welcome to the forums!

I have followed the guide at https://theautomationblog.com/getting-a-b-plc-data-into-a-raspberry-pi/ a time or two for testing with RPi but never in a permanent environment. The viability of RPi in an industrial setting is still up for debate. But I digress.

The 1200 series is an oddball with the release date and version making a difference in the comms options.

You may need a 1761-NET-AIC to communicate via RS485, as a ton of 1200's (Or all?) didn't support RS485 DF1 out of the box but needed RS232 - 485 conversion.

Welcome to the PLCTalk forum community !

The MicroLogix 1200 has only RS-232 type serial ports, regardless of model or revision. Two other MicroLogix models (the 1100 and 1400) have both RS-232 and RS-485 built into the same connector.

In order to use an RS-485 interface you will need some kind of converter; the 1761-NET-AIC is the standard one from A-B.

I would recommend instead using a USB/RS-232 interface on your Raspberry Pi, and an ordinary 1761-CBL-PM02 cable.

Using the standard 1761-CBL-PM02 cable also eliminates any risk of accidentally connecting to the +24V pin in the serial port, which is there to power accessory devices.

I just checked the contrib-pccc nodes for Node-Red and that only appears to support Ethernet, not a serial connection.

So Step 2 is going to be to be sure that the MicroLogix 1200 supports Modbus RTU Slave and configure and test its serial port.

RS485 is only a physical layer that needs to be used if we have to connect several devices using the Modbus protocol.
From the ML side you need the RS232-RS485 interface, and from the PC side USB-RS485 (or RS232-RS485 if we have a physical RS232 port)
If we have only 2 devices to connect: PC and ML1200, then from the PC side we need a USB-RS232 interface (if we do not have a physical RS232 port) preferably on the proven CH340.
The Master can be ML1200 or PC - it depends what we want to achieve.
Of course, you can use the proprietary Allen Bradley interfaces, but I will pass over their prices in silence.