What significance does 'Net Classes' and 'Load Classes' have in Schematic Editor

Drawing Schematics, Hierarchical Design, BOM, Exporting net-lists, etc.
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Ford Prefect
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What significance does 'Net Classes' and 'Load Classes' have in Schematic Editor

#1 Post by Ford Prefect » 23 Mar 2019, 09:29

Can someone please explain the significance 'Net Classes' (and 'Load Classes') have in Schematic Design and how do they work?
 
NetClasses.jpg
 
I quickly laid a simple schematic with 8 nets.
I then went into 'Objects'/'Net Classes' and added a net class called 'Production' with no other parameters, (`Trace width' = blank/'Clearance' = blank) and I then moved all the nets from the Default to Production- See Pic.1
 
Pic1.jpg
 
I then moved 3 nets from Production to Default and left 5 nets in Production - See Pic.2
 
Pic2.jpg
 
So what has this actually done and does it have any significance with PCB Editor/PCB Layout?
 Thanks :)
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Last edited by Ford Prefect on 24 Mar 2019, 09:57, edited 3 times in total.

Tomg
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Re: What significance does 'Net Classes' and 'Load Classes' have in Schematic Capture

#2 Post by Tomg » 23 Mar 2019, 10:18

This initializes the basic trace width and clearance settings when creating a new PCB from your schematic. If you leave "Trace Width" and "Clearance" blank in the schematic, those fields will automatically be filled with the standard DipTrace default values (e.g "0.2*") when implementing the Convert to PCB tool with its "Use Schematic Rules" option. All nets need to have initial width and clearance values assigned to them.

The Load Classes tool will import the values found in another file of your choice into the schematic.

Notice the "Advanced net class properties and class-to-class rules should be set in PCB Layout module" suggestion in the Net Classes dialog window. After net classes have been set in the PCB layout (and the PCB file has been saved), you should use the Load Classes tool in the schematic (point it to your PCB file) to import those values. Don't forget to resave the schematic after importing.
Tom

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Re: What significance does 'Net Classes' and 'Load Classes' have in Schematic Capture

#3 Post by Ford Prefect » 23 Mar 2019, 11:06

Thanks for reply Tomg, but...
Surely you can just create a schematic with components and wires etc. Then do a convert to PCB to get the ratlines and components into the PCB Layout..
Then do either a auto-routing or manual routing and add/adjust the traces in Trace Templates..
Then within PCB Layout change the traces to the specific traces you want based on the traces that have been set up in the Trace Templates.
So the end result is what you ultimately produce with PCB Layout, and schematic editor is just used to help your circuit get into a PCB design within with PCB Layout.
I am thinking that a schematic is just a design of components, wires etc. all connected together to form a circuit.
I still cannot what significance 'Net Classes' and 'Load Classes' have.
Am I missing something?

Tomg
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Re: What significance does 'Net Classes' and 'Load Classes' have in Schematic Capture

#4 Post by Tomg » 23 Mar 2019, 13:18

I'm guessing Load Classes would help speed up the process of initializing a new project if you need to create another circuit with identical net classes and differential pair assignments. As for the trace width and clearance settings, probably not necessary in the schematic unless you want to make sure that the PCB routing doesn't start out with traces and gaps that are too narrow or wide. Other than being one less step to worry about when creating the PCB, I don't know why the width and clearance settings are available in the schematic.
Tom

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Re: What significance does 'Net Classes' and 'Load Classes' have in Schematic Capture

#5 Post by Ford Prefect » 23 Mar 2019, 16:15

 
Umm, :? maybe Stanislav or one of the other Technical Support people can give a full and detailed explanation (with possibly examples) of how this works and how it is used as I am unable to find a reference to 'Load Classes' in the PDF tutorial.
 
 

farley
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Re: What significance does 'Net Classes' and 'Load Classes' have in Schematic Capture

#6 Post by farley » 24 Mar 2019, 07:27

Surely you can just create a schematic with components and wires etc. Then do a convert to PCB to get the ratlines and components into the PCB Layout..
Yes. I do this all the time for simple boards. You do not need to use the net classes feature at all. The trace width for each net can be individually set in the PCB Layout module.
...I don't know why the width and clearance settings are available in the schematic.
Sometimes the person designing the schematic and the person doing the PCB layout are not the same. I would suppose having these settings in the schematic module lets the circuit designer document any special considerations for certain nets.

Tomg
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Re: What significance does 'Net Classes' and 'Load Classes' have in Schematic Capture

#7 Post by Tomg » 24 Mar 2019, 08:13

"...I am unable to find a reference to 'Load Classes' in the PDF tutorial..."

The only reference to "Load Classes" I can find is in the schematic help file under [+]Schematic > [+]User Interface > [+]Main Menu > [?]Objects, which states...
"Load Classes – load net classes from previously saved rule file (*.rul) or directly from any layout file (*.dip)."
Tom

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Re: What significance does 'Net Classes' and 'Load Classes' have in Schematic Capture

#8 Post by Ford Prefect » 24 Mar 2019, 08:44

Tomg wrote:
24 Mar 2019, 08:13
The only reference to "Load Classes" I can find is in the schematic help file under [+]Schematic > [+]User Interface > [+]Main Menu > [?]Objects, which states...
"Load Classes – load net classes from previously saved rule file (*.rul) or directly from any layout file (*.dip)."
Yes, that is all that I could find, but that's it!
It does not go into any detail about what it actually does, how it is used and it's ultimate objective or intention.
It would just be interesting (to me and no doubt everyone) to learn if it's useful or just a redundant command.
 

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