Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Schematic symbol Active lows and naming conventions

Status
Not open for further replies.

Mikebits

Well-Known Member
Long title I know. I am just wondering your thoughts, and or how you do things when it comes to schematic symbol pin names. Mainly active low pins.

In my experience and in the past, I have always used inverter balls for active low signals, ie. -o, and this seems to be standard practice. Now with the pin, we add a pin name, for example out active low signal is a chip select, so it is common to see /CS or CS/ where the slash also indicates a active low and is useful for off page nets. In the schematic you would see |0- CS/ and somewhere on another page you might see a net ----->CS/

So here is my problem, my lame schematic capture software does not accept the / for a pin name or net name. I can place inverter balls for the pins, but for off page nets where the inverter ball is not seen then the name is more important, as I always like to know if a digital signal is active low, or high.

What I am currently doing is naming my nets with the following rules.

  • Caps are used for all net names and IC pin names, Example: RD or WR
  • An exception to the above rule is if the signal is active low, then the net name is in caps with an _n added as a suffix, Example RD_n(n for Not)
This may seem anal or even silly as I could simply name the net RD and the schematic would still be correct and pass all tool design rule checks, however, and I think this is important, by adding CS/ or CS_n, a person other than me reading my schematic can look at the schematic and know that the CS pin is active low. I think these small details aid in following a schematic and assist in debug.

So, I ask, do you usually just make net names ignoring the signal state (active state), or do you follow a similar naming convention, and if so, what naming convention do you use?

Thanks
 
I made one error in my above post. I can give my symbol pin names a slash like CS/ but I can't name nets with a slash.
 
I use a ~ (tilda) as a suffix. LTSpice did us a huge favor by allowing almost any symbol in a net name...
 
What is the lame schematic software that you use? Last I recall, you did not use Eagle. However, in Eagle, just precede the name with an exclamation mark like this: !CS . That will then show with a line over the symbol meaning active low. For nets, it will show like it is written, e.g., !CS. For pins, it creates a line-over, like this:

upload_2015-9-1_6-1-57.png


John
 

Attachments

  • upload_2015-9-1_6-1-45.png
    upload_2015-9-1_6-1-45.png
    1.6 KB · Views: 176
John, that's actually cool. So it adds the line over the net name, what would the name be in the net list? Would the net list just have CS, or !CS, or what? Just curious. The software I am using is Multisim Blue Premium edition. I paid for a year license, so I am stuck using for at least a year, and hopefully I can move to a better package. One of the things that I like about Multisim is the symbol library has a Mouser data base, so when the BOM is created you can place your order to mouser directly from Multisim. I have not tried this yet, but it sounded convenient. I have found quite a few annoying things in using Multisim, but that's the way it goes.
 
Here's a silly example:

upload_2015-9-1_18-49-48.png


It is easiest to use when making a device. BTW, The origins show for grabbing and moving. They don't generally print. I used screen capture, which is why you see them.

Here's what a snip from a print looks like:
Capture.PNG




John
 
Last edited:
LTspice will also convert a leading underscore to an overbar.

One potential problem though....if this is done for a wire label (net name), the leading underscore is also contained in the netlist. This might cause problems with other simulators. So...if compatibility with other simulators is important, might be better not to use special characters.

Just something to consider.....
 
I have also seen some people use apostrophes ' to signify "not":

'MOSI
'MISO

The downside to this is that apostrophes are sometimes difficult to see, and may be missed.
 
Does that character create a line-over in the programs you have used? I thought Mikebits wanted something that would result in the widely accepted line-over in whatever drawing he is working on.

Later the issue of exporting netlists to a simulator came up. I do not have the current Eagle simulator plugged in, but the net list created by Eagle is "!<name> ." I presume its simulator tolerates that, but have no ready way to test it.

John
 
Does that character create a line-over in the programs you have used? I thought Mikebits wanted something that would result in the widely accepted line-over in whatever drawing he is working on.

Later the issue of exporting netlists to a simulator came up. I do not have the current Eagle simulator plugged in, but the net list created by Eagle is "!<name> ." I presume its simulator tolerates that, but have no ready way to test it.

John

I may have misunderstood. As I read it, he was looking for a way of labeling nets as "Active Low" using plain text when slashes are not allowed. I am not aware of any software that converts an apostrophe to a bar, if that is indeed what he is asking.

Altium has you use a backslash following each character that you want a bar over.
 
No Derstrom you did not misunderstood, you are correct. John what is up with input lines going through the body of your gate?
 
Didn't you understand what I meant by "silly?" That was not the point of the illustration.

John
 
Sorry John, I was just not sure if that's how Eagle drew the symbol.
 
hi micbits,
i was reading help from eagle.
based on context. I typed active low
at some place i got this .

Overlined text
Text can be overlined, which is useful for instance for the names of inverted signals ("active low", see also NET, BUS and PIN). To do so, the text needs to be preceded with an exclamation mark ('!'), as in

!RESET

which would result in

_____

RESET

This is not limited to signal names, but can be used in any text. It is also possible to overline only part of a text, as in

!RST!/NMI

R/!W

which would result in

__

RST/NMI

_

R/W

Note that the second exclamation mark indicates the end of the overline. There can be any number of overlines in a text. If a text shall contain an exclamation mark that doesn't generate an overline, it needs to be escaped by a backslash. In order to keep the need for escaping exclamation marks at a minimum, an exclamation mark doesn't start an overline if it is the last character of a text, or if it is immediately followed by a blank, another exclamation mark, a double or single quote, or by a right parenthesis, bracket or brace. Any non-escaped exclamation mark or comma that appears after an exclamation mark that started an overline will end the overline (the comma as an overline terminator is necessary for busses).


I hope this helps you.
regards
 
Here is a trial of two chips where one is active low and another edge active low. I just used "abc" for net names . later I used names and typed "!xx" and it has created over score , Mikebits.

Japanhalt (thanks) has already identified this and I just created One .
 

Attachments

  • active low naming eagle.pdf
    10 KB · Views: 164
Hi Sarma, thanks for the info, but I do not use Eagle. I was really asking what naming conventions people usually use on their schematics. The usual convention I have seen for active low is to use a slash / but since my software does not allow the / I have been using _n.
Thanks
 
Got it.
all the best
perhaps if it is permitted you could use Underscore that could be possible , if not Overscore.
i see people using"*" and also "/"
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top