How to register Cloud Fieldbus as a device in your Cumulocity IoT tenant.
Cloud Fieldbus is a concept that integrates several protocols into Cumulicity with the ability to remotely control which data points are read from the respective protocol and how to map them into the platform. You can read more about this here: Cloud Fieldbus - Cumulocity IoT Guides
In order to use the Cloud Fieldbus with a device, you need a device that supports it.
Is there any other way without the physical device?
like a simulator or something
Well then the question becomes what do you want to simulate?
Do you want to simulate the data in Cumulocity that such a device would create? Then you can use the built-in simulator to create measurements, alarms, and events as you desire.
Do you want to simulate the connected Fieldbus protocol like Modbus? Then you need a Modbus simulator of your choice. Additionally you need a device or piece of agent software that supports Cloud Fieldbus.
How to get/create modbus simulator?
The modbus protocol and any simulators for it are outside of the scope provided by Cumulocity. There are several open source and commercial options available online. I cannot recommend any one software in particular because I haven’t personally verified them. You’ll have find the one that fits your use case best on your own.
This could be a start: modbus tcp simulator - Google Search