Learning about communictions 1

[MThomas]

I'm looking for some advice on where to go to learn about communications. I've recently started working for a company that manufactures AC drives, and they want me to eventually become the "resident expert" on communications.

Now when they say they want me to become an "expert", they're talking about everything external to the drive (CAN, DeviceNet, Fieldbus, Modbus, etc.) and everything internal to the drive (SPI, I2C, etc.).

Admittedly, this is not my field. I focused on control systems in college. If there were books out there like "Modbus for dummies", I'd probably start there, but I've not had any luck hunting down such titles.

Could someone here be kind enough to point me in the right direction to get started on such a huge task?

Thanks,
Mike

 

[Skogsgurra]

There are really many aspects on this.

There is not one single book that covers it all. But there are several manufacturers of ICs for different protocols and technologies. Their application notes are a good start. Search the home pages of Freescale, National Semiconductor, Maxim, Texas Instruments and many others. That will give you some insight in the inner workings.

I think that you should just learn basic RS232 and 485 first. The protocols are similar but the hardware differs. This will take some time. And while you are doing this, you will read about other technologies and pick up references that will take you further.

The manuals for different makes of VFDs often contain very down-to-earth information on protocols and how to set up a bus. The Profibus is what I personally would start with. There are profiles for drives and automation and Siemens has good (free, on

http://www.siemens.com)

literature on that.

One tip: Do not try to master it all at once. And do practical experiments parallel to your reading. That's the best way to learn.

Gunnar Englund

http://www.gke.org

 

[itsmoked]

skogs has some really excellent info there... Read it more than once!

Most of those protocols you mention are actually fairly similar. So as skogs sez start with the basics. The widest reaching(probably 100:1) methods of RS232 and RS485. These are only signalling standards which describe the electrical properties required. The user then has to provide a "data protocol" or framework with which to work in. If you want the "current" how does one ask correctly for it and how do you respond? That is the protocol.

A lot of these newer methods are just standardized protocols. "'PC027' always means current" in protocol X.

So once again, once you understand the basics and how a few products use it you can start to see the 'why' of these higher level protocols and their schemes will be easier to understand.

I would follow this learning plan:
What is RS232?
What is RS485?
What is RS422?
How do two different VFD makers use these.
What are the general protocol schemes used by these two VFD designs to communicate data and commands.

What is Ethernet?
What is the general protocol of Ethernet communications, the big picture?

What is DeviceNet?
What is Fieldbus?
What is Modbus?

Once you have this stuff packed into your head step back and examine SPI, I2C. Just web troll for this stuff it is everywhere. These signalling methods are almost exclusively used inside of a product. Rarely if ever are they used to communicate outside of a product. They usually are straight logic signals unacceptable for driving cables etc.

Once you have a grip on these then look at CAN. CAN is an oddity. Once you understand the others you will see the 'why' for the oddity.


Oh, and somewhere in there buy a two year subscription to Circuit Cellar Magazine as they constantly cover comm protocols.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MThomas]

Thanks, guys! This is the direction I was looking for. I appreciate your replies!

-Mike

 

[MacGyverS2000]

I think Circuit Cellar still sells CDs of their back issues for much cheaper than a typical book. They'll cover enough of multiple subjects over a few years' worth of CDs to make it worth your while, then grab a detailed book on the specific ones that interest you.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

Google the name and/or designation of the communications standards that you're interested in, but add the search term '.pdf' to your search. This will tend to float some very interesting handbooks towards the top of the results.

With luck, you'll end up with a nice collection of free e-books from various OEMs.