Hi,

I'm looking for a description of the modbus RS485 connector. We are going to make a cable to connect an RJ45 connector in an Optidrive to the RTU modbus connector.

Best regards, Martin van der Bij

Hello Martin;

In RS 485, the "RS" means "Recommended Standard", which has been interpreted this way over the years: the standard is not enforced and manufacturers often design their own pinouts on their RJ45 or DB9 connectors for their communication partners. You have to be very clear on the equipment you have in order to build cables between master and slave.

Just as an example from Invertek: depending on the software version on the Optidrive you want to connect to Modbus RTU, you have 2 very different pinouts for RS 485 connections on the RJ45 connectors. See the attachment below.

So please look at the manual for the model of Optidrive you have and give us the exact pinout you will be using. And tell us what Siemens equipment you will be using as a Modbus RTU master, so we can search for the exact pinout and connector type for that module to create a cable to the drive.

Notice in the attachment below that if you have more than one drive you will need RJ45 splitters to connect one drive to another.

Hope this helps,

Daniel Chartier

Hi Daniel,

Thanks you for the quick reply, i have been given this image to connect the optidrive.

Regards Martin

Hello Martin;

This is good, it showns one end of the cable connection, on a RJ45 connector.

Rx/Tx+ on pin 5;

Rx/TX- on pin 4;

GND on pin 3.

Now: What goes on the other end of the cable? What will act as master on the Modbus RTU link?

Hope this helps,

Daniel Chartier

Hi Daniel, excuse me for the late reply.

The Siemens IOT2040 is going to be connected to the Optidrive. Since i want to controll the Optidrive from the arduino environment trough the RS485 port, i think the IOT2040 is going to be the master of this setup.

If you have any sugestions to make a compatible cable that would be very helpfull.

Regards Martin

Hello Martin;

The IOT2040 manual gives these informations on RS 485 connections.

https://support.industry.siemens.com/cs/attachments/109741658/iot2000_operating_instructions_e_en-US.pdf?download=true

See the screenshots belos.

However, it gives no information on the availablilty of Modbus RTU protocol...

Hope this helps,

Daniel Chartier

If i understand it correct, the cable should have 3 wires, and connected like my attachment?

Regards Martin

Hello Martin;

The wiring looks good to me for RS 485: + to +, - to -, Gnd to Gnd.

Hope this helps,

Daniel Chartier