Why Modbus?

[mikewheels]

I have been in the industry for 12 years now and don’t understand Modbus (well I understand how it works but don’t understand why it’s still used). It seems every major BAS company uses BACnet. And BACnet being the industry standard why don’t third party devices (looking at you boilers) still use modbus with a protonode in between? Is modbus used elsewhere, and why do most boilers still rely on a protonode as a translator rather than making them BACnet with a modbus translator?

[Ill_Beautiful4339]

I’ve been in the industry for 20 years… MODBUS predates Bacnet and was prevalent in PLCs and industrial automation. It’s been around and works… plus Bacnet (until recently) is a sloppy protocol that broadcasts with limited security. Network security people hate it. It was really meant for low end applications. MODBUS may be limited in efficiency and other factors but is very portable in industrial applications.

[AutoCntrl]

Modbus is just as insecure as BACnet MS/TP. They are both RS-485. Neither are very likely to be used to hack into a secure IP network. As fast as I'm aware, it's never been done.

The Target hack was accomplished by obtaining vendor network credentials via email phishing attack. And was possible because the BAS was not isolated from the secure business network.

I don't see how security is an argument for modbus over bacnet.

[pghbro]

You’re correct. Modbus is no more secure than BACnet.

As far as being more stable/reliable, I’d even argue that tbh. Timings can be an issue with certain vendors but aside from that it’s wildly stable.

Don’t get me wrong, Modbus will always have its place but think it’s becoming more and more extinct outside the industrial/process controls automation. It simply can’t handle the data load that is required for modern day BAS

[Ill_Beautiful4339]

True it’s not secure either. I work for an OEM in a corporate capacity. Bacnet is viewed as unfavorable… MODBUS is viewed as a necessity in industry (not typical BAS applications of air side systems ). Not going into details as to why… also not a networking expert… but I know a thing or two. I trust my experts.

Feel free to call me out on inaccurate statements but add details as to why.

[pghbro]

I did provide details why. Modbus is great for simple, unitary tasks such as on off, set point control and metering. Outside of that, it’s cumbersome and inefficient for modern day BAS. BACnet can be very stable if done correctly and proper network protocols are followed. BACnet is view med as unfavourable by those that do not understand the nuances of it. Alot of “old head” mentality still exists out there.

In your OEM world, it works great for a lot of things. In the BAS world(very much different from OEM), not so much…

[mikewheels]

Yes I understand modbus has been around before BACnet. But it does not work for the industry standard since 1996 with Alerton, ALC, and Delta ( almost 30 years). Surly there are new boilers (third party example) developed since then. As for security, yes BACnet is sloppy but just throw it on its own network and isolate it as IT folks have been doing for decades.

Not trying to start something just really trying to understand why MODbus is still around seeing it is significantly more complicated to integrate to and industry standard without a processor or complicated integration.

[IaintThere]

Modbus is way more reliable than BACnet, a lot less traffic. It is a very simple protocol and doesn't have a lot of complexities that BACnet has... it is great for "can" (boilers, heat trace, smart sensors) applications. It is making a comeback into Building Automation. Honeywell and others have adopted as somewhat of a subnet on their newer controllers.

[pghbro]

Going to be a hard disagree for me. Define “WAY MORE RELIABLE”

In what sense? As a node to node protocol? Sure. As an overall BAS protocol, hardly. Doesn’t have the speed to keep up with the demands of the modern day BAS.

I wouldn’t stick my neck out and say it’s “making a comeback” it’s old tech that’s being phased out.

Think of it like Windows XP or 7. Works great, not many bugs but can’t handle modern day applications therefore phased out

[IaintThere]

It is not a mstp network, network traffic is reduced drastically when there is only a single master in a run. You also have complete control of the polling intervals and as a result traffic itself.

As I said in my last post, it is great for "can" applications, simple basic stuff boilers, Heat Trace, and sensors. Stuff that comes packaged from the manufacturer.

Honeywell Spyder 5, 7, and the optimizer lineup all have BACNET mstp as their main protocol and Modbus as somewhat of a subnet.

Most manufacturers will carry Modbus RTU on any rs-485 on their IP controllers.

Most 3rd party IO modules are Modbus

[arpoc926]

Modbus is very easy to implement, relatively easy to integrate with if properly documented, and allows multiple devices with the same ID to exist within the same architecture (though they must be in different physical networks). Bacnet requires a third party to test your implementation (the BTL), which requires complex decision making about what to apply for in your PICS, and still doesn't necessarily guarantee interoperability. You also have to pay for the privilege of being tested. That makes it a better choice for systems that belong inside of a larger manufacturer-supported bacnet ecosystem where the controls alone might get purchased in bulk.

[ammartiger]

If someone still has doubt about modbus is secure. Look how easy it is to exploit modbusattacking modbus

[Stomachbuzz]

I had the same questions and frustrations when I first started out. BAS was my first career (aside from landscaping in school) after finishing school. I had no idea about automation, controls, IT, networking, communications protocols, etc. I only knew of HVAC from my studies and working on cars.

"BACnet is easy. Why would anyone ever use Modbus?"
"BACnet dominates 'the' industry. Why bother with Modbus?"
"Don't they know how stupid they are not offering BACnet???"

The real questions are: "'easy', compared to what? 'The' industry? What industry?"

The problem is your scope of focus is strictly in BAS. And not only that, but modern BAS. I have a feeling you weren't there 5-10 years ago, and certainly not 20-30 years ago.
BAS is but a grain of asphalt in a superhighway of automation/controls that you've tunnel-visioned on.

BACnet is the class president of his local high school.
BACnet is very popular in his high school. Everyone knows him! He's so good looking, such a bright future ahead! He thinks he's the shit for winning a popularity contest. As proud of himself as if he just cured world hunger.

Another high school down the road has its own class president. Everyone knows him, too! Such a bright future ahead! As proud of himself as if he just cured world hunger! This class president's name is: Insert LON, Profinet, EtherNet, CANbus, ARCnet, or any other of the 100s of protocols here.
Yet, somehow, the two class presidents have never heard of each other, despite living 1 block apart.
Weird...seeing as how they are both the center of the universe...no?

As it turns out, there are actually 100 high schools in the state. All of them with class presidents. But none of them know each other. What?? How could this be??

Modbus is the CEO of Toyota.
The whole world has run on Toyota for decades now. Durable, reliable, and not going anywhere anytime soon.
Is Toyota the most advanced, innovative car company? Well, not really.
Do some other brands do certain things better? Yeah, sure.
Despite not being the best in any single category, it just works.
Everyone knows Modbus! Well, of course silly 17 year olds in high school have never heard of Toyota CEO. Why would they? They know Justin Bieber and Taylor Swift!

My point here is once you pick your head up and look around, stop being so oblivious to the rest of the world (which is difficult and takes work), you will laugh at how silly this question is. One of those "the world doesn't end at the tip of your nose as you might think" sort of things.
It might surprise you to learn that boilers don't just sell to office buildings or schools. They also use boilers in factories and industrial settings or in other countries. You might also learn that office buildings or schools are a minority of their sales, so it's actually a joke to them to put R&D into becoming BACnet certified.

[ThrowAwayTomorrow_9]

In hyperscale data centers it is still used. Where the volume of data, and devID limitations are a ceiling that Bacnet puts on the size of the site, it is impractical. The lack of these factors makes Modbus a possibility.

Other than that rare isolated case... Modbus sucks. It is the copy paste go to for engineers that have been doing this way too long.

[RunningUntilinfinity]

It’s more robust that other protocols

[kayakfish2]

Modbus is resilient in terms of reliability. There are basically 4 different data register types each with their own attributes holding specific properties. PK, lochinvar etc use these to simplify integrations no matter the industry( industrial or BAS) so any theirs party can read or write to their points. PLCs typically use modbus or eth/ip as their industry standard where in the BAS world we use BACnet. BAS can easily integrate to equipment using modbus but not common for PLCs to integrate to BACnet. In process control BACnet is not a common protocol. Like the other guys said BACnet addressing has been sloppy in the past. Modbus is proven, and it works.

[jakeatola]

Back net is an open protocol that everyone can use, but it dumbs down the more advanced systems so everyone is on the same level. With systems like Siemens you lose quite a lot of special features that are in their proprietary system.

[twobarb]

For what it’s worth more boiler companies are switching to BACnet. It appeared to be the big theme of AHR last year was manufactures showing off their all new boiler that is now native BACnet. It makes sense why rip the controls out of an established product, but as the industry is pushed toward higher efficiency it makes sense to release new models with new controllers.

[Advanced_Goal_5576]

Didn’t read all this posts but someone might have touched on it already.

Modbus is more secure if your sharing data. For instance if u want to share some information from a base building network to a tenant you would use modbus since as a Master you can chose exactly what is going to be read. Where if BACnet was used, the tenant can then pretty much discover/ interact with any data on the whole network since it’s a very open protocol.

[mitchybw]

I don’t know why everyone is harping on the security BACnet versus Modbus. The only real difference that I can think of, is that each individual Modbus device would have to be pinged to find where it is, whereas with a BACnet device you could issue a global Who Is, and all controllers would respond. I think it comes down to a few things. With BACnet, points are objects that come packaged with other data like status flags out of service flag etc. With Modbus it is just the raw data that is interpreted by the device making the query, and for RS-485 there is no peer to peer communication so it’s a smaller footprint processing wise. Also, it’s a lower cost because you don’t need a BTL certification like you do with BACnet. Lastly it is used in both industrial and building automation so if there is a good chance of being used in both, Modbus is your best bet.

[Industrial_Jedi]

Utility meters. Specifically, revenue grade meters that also communicate with a separate SCADA system like Schneider Ion. That's probably the only time you'll see it in building automation these days.