Convention for inverted signal

Question

Is there a standard convention for marking an inverted signal using only text? The package currently being used does not support having a bar over the signal in all instances.

IE: NOT_Reset or Reset_Bar etc? when you can't use \$ \overline{Reset}\$

Answer 1

Often a tilde ~ is used to indicate negation (just like the bitwise NOT-operator in the C-programing langage) if only text without special formatting, like overbars, can be used.

E.g. ~reset

Answer 2

I often use "/RESET" using the forward slash to indicate active low

Answer 3

I use NOT_ because it's clear what it is if I forget the convention or whoever is reading it doesn't know the conventions. But I am also very verbose in my labeling. Principle of least astonishment.

Another reason is that it's difficult to miss when reading and difficult to forget when typing. I never liked things like a single character prefix (and a suffix is even worse) because it's way too easy to gloss over when reading it and interpret it as an uninverted signal, or when typing it out too (especially if it appears in code and you have the uninverted variant also floating around)

Answer 4

There are many languages and logical forms of expression. Since schematics are also "logic diagrams" , they too express the standards adopted by the international or corporate community.

They must also beware of the limitations in character set and ability to draw vectors such as "overline" unlike "underline" which is available in some.

From a historical point of view for documentation on signals used in both limited character sets for say "Theory of Operation" and schematic drawings, the most common symbol I have seen since the early 80's was the ! symbol placed either before or more often after the word to indicate "Negation" or the active state is low.

e.g. reset! is active low. Similarily I have also seen reset~ , /Reset

A or A! are the binary states for normal and inverted signal or in Boolean logic A=1 and A!=0

! is also called the Bang key .

Here are all the software variants which includes examples of "negation" may not be relevant to schematics but may be familiar that use extended character sets.

Answer 5

I usually use a preceding exclamation mark:

!RESET

The main reason for this is I can easily denote signals like this:

UP/!DOWN

Answer 6

I've seen all kinds of conventions:

• RESET-
• RESET_L
• nRESET

Just pick one and use it consistently.

Answer 7

Check you coding environment documentation to determine if you need to code active-low signals a certain way.

I typically code HDL using the convention reset_n or resetn. However, one development suite I use regularly will sometimes get confused if I don't use -only- resetn; it does not interpret reset_n as one might expect during its parsing and autogeneration stages.