Multichannel Differential pair Net naming! - Page 1
Forum section: electronics / general

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 22, 2020, 11:46:23 am
content: Hi,I have a design with several RS422 parts in it, I want to know what's the best way of naming nets, so that I can use the multichannel and Differential pair classes at the same time.I have done something like this,But I think I have done the naming in the wrong way.

author: Pseudobyte
author_rank: Frequent Contributor
timestamp: April 22, 2020, 01:39:40 pm
content: Not far off i think you are just missing the bus entry on the output side.Top Sheet:Sub Sheet:One Compiled sub sheet:Your compiled names may not look like mine, if you need help sorting that out let me know.

author: Pseudobyte
author_rank: Frequent Contributor
timestamp: April 22, 2020, 01:42:25 pm
content: I forgot the diff pair class but you could put that anywhere and it should be applied to the physical net.

author: ajb
author_rank: Super Contributor
timestamp: April 22, 2020, 07:18:49 pm
content: Splitting diff pairs into N and P buses might work, but it's a pretty gross solution. I would probably skip the REPEAT() syntax and just place five separate instances of the sheet symbol in the top level sheet. That will still allow you to use multi-channel features in the PCB but gives a lot more flexibility in how you hook up the schematic. I might also use a harness for the diff pairs, the way that harnesses are named by default should allow the diff pair rules to work as you'd expect since the harness name gets prepended to the harness entry name. You might need to adjust your net naming settings in the project settings to make sure that nets get their names from the correct part of the schematic structure.

author: javad2040
author_rank: Contributor
timestamp: April 26, 2020, 01:51:16 pm
content: I have the same problem with a multichannel DDR3, guys do we have a solution?

author: ajb
author_rank: Super Contributor
timestamp: April 26, 2020, 09:34:35 pm
content: As a rule, if the question is "How do I do X with a repeated schematic symbol?" the answer is "By not using a repeated schematic symbol". The "repeat" syntax breaks down quite quickly when you either have to meet a particular net naming convention or have to break out a lot of individual signals from the repeated block as both the OP's question and the DDR3 question illustrate.In the DDR case I would consolidate a lot of those signals into one or more harnesses (with the harnesses brought out by ports/sheet entries), place four separate instances of the sheet symbol, and break out the components of the harnesses to get the busses and discrete control signals hooked up as needed. Note that unlike buses and 'repeat'ed sheet entries, harnesses can be hierarchical, and can contain other harnesses or busses, so you can package up a whole mess of signals into one neat line on the schematic, then break out from there as needed. You can wrap all of this up into an intermediate sheet if you don't want to clutter your top level sheet.Note that multichannel features in the PCB editor will still work with multiple instances of the same sheet even if you don't use the repeat syntax, so the only thing you lose by not using repeat is some extra space on the schematic, but you gain a lot of flexibility in how you can hook things up.

author: KaneTW
author_rank: Frequent Contributor
timestamp: April 26, 2020, 09:46:42 pm
content: Yeah, I've used REPEAT() a bunch since my software engineer ass really loves the concept, but it just doesn't work that well.Also ran into really, really annoying "copy room layout" bugs, but that's unrelated to REPEAT() (Some parts were copied with a slight offset, leading to jumbled traces of various width and other fun stuff --- ended up deleting the room and copying manually, then relinking)

author: sean0118
author_rank: Frequent Contributor
timestamp: April 28, 2020, 04:25:20 am
content: Quote from: KaneTW on April 26, 2020, 09:46:42 pmAre you sure the rooms you were copying between were exactly the same size?

author: KaneTW
author_rank: Frequent Contributor
timestamp: April 28, 2020, 03:14:56 pm
content: Fairly sure. I resized them all to the same size before starting the first layout.

author: Pseudobyte
author_rank: Frequent Contributor
timestamp: April 30, 2020, 01:38:04 pm
content: Channel offsets need to be the same otherwise copy format does not work. So if you annotated poorly in the schematic or did not plan for multichannel it likely will not work correctly.