Modbus Part 1

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1 hour 22 minutes
Video Transcription
I see a Scott of fundamentals in this segment, we're going to look at mod bus, Part one
in the learning objectives for this particular module. We're going to get an introduction of what the Mod Bus protocol is. Some of the limitations with mod bus, where mod buses actually used and some of the equipment that uses Mont bus itself.
So it's an industrial control system protocol and eyes, actually a registered trademark of Modica Lon Schneider Electric. It was invented in 1979
and openly published, which means it's not proprietary. And that's one of the reasons why it's so widely used. You do not have to pay a licensing fee to use it. You can just use it very much like an open source protocol.
Now what it does is it enables communication between industrial equipment all but it must be on. The same network
could be used to connect n transmit, also between a supervisory system and what is called an arty, you remote access terminal unit with a supervisory control and data acquisition device, which is what Scott actually stands for.
Very similar to firewall technology, it uses what's called ladder logic. So all of the settings have to be done in a certain ladder manner from top down. It is a slave to master based architecture,
and it uses two different transmission modes, either asking or what's called our to you.
Some of the common equipment that uses mod bus There's a programmable logic controller, the remote terminal unit. Ah, certain motives actually used mod bus. There are gateways for mod bus, which can also transform on bus to other protocols as well. There are
a certain amount of,
uh, older, usually safety equipment that can actually use mod bus and also SCADA systems themselves.
Now there are some limitations with this particular protocol. When you're dealing with PLC's,
it's gotta understand how to operate with a PLC now. Another limitation is there's no method to understand the description of a data object. So what happens is if you have a sensor. Mod bus doesn't really work with these things with the temperature sensor because it can actually send back the information
of what the temperature is. It is a master to a slave architecture. In addition to that, if you've got a field device which are rather common, it can't report an exception
Masters the master portion using Mod Buster required to poll devices and report changes. But what happens is it will send that polling to the entire network of mob us and every device will actually see it.
It doesn't go just directly to that one device. So what happens is
it can consume a lot of band with on what is typically lower band with networks.
And it's also limited to 254 address devices on one datalink. Because all of these things have to be on the same network,
transmissions must flow in the same manner across the entire network where they're connected. And there's no security
now when I say there's no security the way that mod bus was written, as it will take ah, command without authentication as long as it is properly formatted from anywhere. And this could be dangerous because that also can expose mod bus to manipulation.
As some of the protocol versions within my bus itself, there's my bus are to you far to use.
There's asking there's one called TCP. Then there's one that can take mod bus over boat T C P R T you, and also I p networks. You can also send us mob us over UDP.
There's also a bit of ah mixed type of protocol variant called mod bus. Plus,
there's also permits Mont Bus and Enron Lot bus
now with mod bus are as 45 which is another variant on Lee. The master itself can actually initiated command Command can't come from a slave to a master or a slave to a slave.
And what's unfortunate about this is that, um
because a command will go from the master,
it will spread to all of the slaves. And, uh,
slaves have to respond to any sort of request or command I can also use with this connector type are to you asking and plus
now there's also another variant called mob us Ethernet, and it uses TCP. And this is where it gets into a little bit of cell. Where can operate on the highest M band and also for SMS is which are typically used to other people
inside an automation environment, sometimes building automation. So if there's a problem with
an elevator, in some cases of it happens to use mod bus, it can actually, uh, tell you over SMS. If there's a problem. Some older fire safety systems and general alarms can also be sent
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