How to define different Communication


Thread Starter


I am always confused what is the difference between H1Bus and Profibus. Difference beween H1Bus and Ethernet. and Difference between HIbus, ethernet, profibus, TCPIP.

Please can anybody there to explain it to me in simple words? I need to know more in detail. Please help me. There lot of technical personnel visiting this site. I hope I will get favorable answer.
thanks to all.

Daniel Chartier


Sorry, I don't think anyone will be able to answer your question "in simple words". This is almost like asking for the differences between French and German... Here you will find links to most major fieldbuses on the market:

Each industrial network was designed using different physical layer supports (twisted-pair, ethernet cable, fiber-optic) and the protocols (master-slave, peer-to-peer, client/server) are too different to detail here. You will have to study each one that is of interest for you. For exampel, you ask about differences between H1 bus and Profibus. I will presume you mean Fieldbus Foundation H1 and Profibus-PA. Both are designed for comms with smart instrumentation transmitters, using the same physical layer (shielded twisted-pair cable), using the same datalink (Manchester-coded communications) and are based on the FISCO intrinsic safety requirements for speed and power levels. They differ in the application level (level 7 of the OSI model), whereas in Profibus-PA communication function blocks are loaded into the main processor, and on FF H1 these are loaded and instanciated in the intrument themselves. Confusing? This only means that you need to study them more closely if you need to understand them.

Hope this helps,
Daniel Chartier
Here is my personal opinion one each of the three:

*** I am always confused what is the difference between H1Bus and Profibus.

Explained in a separate posting

*** Difference beween H1Bus and Ethernet.

Ethernet is a physical layer (copper wire, fiber optic, wireless...) and a data link layer (MAC address...)

Ethernet is very fast - several Mbit/s but wire only runs 100 m. H1 speed is a moderate 31.25 kbit/s but runs 1,900 m and can have 120 m spurs and also provides power to devices - even with intrinsic safety or non-incendive for hazardous areas. H1 has the scheduling explained in the separate posing. Therefore H1 is used for 2-wire field devices far from the control room while Ethernet is primarily used among controllers and workstations within the control room.

Ethernet is used in conjunction with TCP/IP or better yet UDP/IP for network and transport layer. In addition to this, you need to select an application layer protocol such as PROFINET, Modbus/TCP, FF-HSE or one of many others built-into control systems. When all put together you get a complete protocol technology. Ethernet alone does not do anything.

*** and Difference between HIbus, ethernet, profibus, TCPIP.

H1: use this for your transmitters, valves, analyzers, etc. field instruments

Ethernet: use this between your controllers, servers, work stations, and to
connect to rest of the enterprise

PROFIBUS: use this for drives and remote-I/O
TCP/IP: is a layer on top of Ethernet when connecting to the enterprise. Within your control system you will likely be using UDP/IP on top of your Ethernet instead.

It is a very big topic. Hard to handle in a single post. To learn more about fieldbus and Ethernet and stuff you did not know about HART take a look at the yellow book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" buy online:

Dear Daniel,
The Manchester encoding is not at the data link layer, it is also part of the physical layer. The Manchester coding merges the data signal with the clock signal so that you can synchronous data transmission at the physical

Foundation fieldbus H1 and PROFIBUS PA have different data link layers (in your analogy PA is only German while H1 is primarily French but with a touch of German).

In my personal opinion, the data link layer is perhaps the biggest difference between H1 and PA. H1 is "scheduled" while PA is "free running".
For H1 the real-time and non-real-time data run in different time slots. The real-time data also uses publisher-subscriber communication while the
non-real-time data uses client-server communication (similar to PA master-slave). H1 also has report-distribution for alarms that fall in the non-real-time slot. By having fixed slots for real-time and non-real-time it
is ensured that varying loads of non-real-time data does not change the response for the real-time control. The second aspect of this is that
real-time-data is precisely periodic (isochronous). The "jitter" in sampling
cycle is minimized. This is important for process control such as PID. This is a long and complex topic but it boils down to e.g. the PID equation including a constant 'dt' for both the I and D terms. Unless precisely periodic the real world 'dt' is not constant...

H1 blocks can execute in a centralized processor or decentralized in the field device. Either way, a third nice aspect with the H1 schedule is that the execution of the blocks is synchronized with the communication. This further reduces control loop jitter and it also eliminates the need for oversampling. This is important because the bus speed is moderate (due to long distance, spurs, and intrinsic safety requirements etc.).

To learn more about H1 and PA take a look at the yellow book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" buy online:


Richard Caro

Sorry Jonas, this time you are wrong. H1 was used by my SP50 committee for the low speed Fieldbus and was continued by the Fieldbus Foundation. (H1 means Hunk 1. We were not too creative in naming this.)

However, Siemens used H1 as the name for an older version of their SIMATIC Industrial Ethernet bus before Profinet was created. The hardware is the same, but there is different software support. It's Ethernet.

Richard H. Caro, CEO
CMC Associates
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Acton, MA 01720-3407
Tel: 1.978.635.9449
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True, the term has history, but if somebody is looking for "H1 bus" today it is most likely FF or possibly the Hummer H1 which is big as a bus :eek:)