What does 3V3 or 1V8 mean?

Question

While reading a datasheet for an IC I came across the pin voltages being presented as 3V3 or 1V8. What does this representation stand for?

Answer 1

That's the new politically correct way of writing numbers that would normally have decimal points. Some parts of the world (Germany for example) use a comma to separate the integer and fraction digits. To avoid ambiguity in international situations, some people now put the letter for the units where the decimal point should be. So "3V3" really means 3.3 Volts and "1V8" means 1.8 Volts.

If your audience is English speaking or it is obvious the document or the context is in English, then you are fine using a decimal point normally. After all, using a decimal point is part of the language no less than the words used to describe other things, so this is not ambiguous. In rare cases when numbers are by themselves without a language context, then it's probably best to use the "3V3" type notation. Otherwise, I personally find this notation rather annoying since I have to look at it and think about it rather than the brain parsing it without much conscious thought.

As with most things PC, it's about choosing which group of people to piss off.

Answer 2

I've always been told that the reason for using letters or symbols in place of the decimal point is neither for international relations or variable names in code but for clarity in print. The issue being that when datasheets were typed up, or schematics drawn, and then copied/photocopied/faxed/etc the dot may get dropped.

This issue obviously isn't such a big deal these days but using 3V3 or 4R7 is still pretty common. It's really common in older documentation here in the UK (and I'm talking back to kind of era where we really wouldn't have creating documents with legibility to Germans in mind...).

I'm pretty happy transposing commas for full stops in European documents, it's fairly common to find them in European publications (even when they've been translated to English).

Answer 3

It's a naming convention to denote voltages. The period is replaced by the V. So, rather that 3.3V or 1.8V you would write 3V3 and 1V8, respectively. It came about for a couple of reasons:

• In schematics which involve a device for which code has to be written (microcontroller, FPGA), many code languages use a period or comma as an operator (for example C uses periods to reference structure members). If this is the case, the names of the signals in the code cannot directly follow the schematic net names to which they are connected as it will cause compilation errors. So this scheme was developed to get around this and allow the exact same net to be referenced in the code as in the schematic, allowing for easier readability of the code and a more accurate reflection between the code & schematic.

• For the reason mentioned above, many schematic editors don't accept periods or commas in the names of the nets because they generate code directly from the schematics or use code to operate directly on the schematics. Both cases can be corrupted by the use of symbols (like periods or commas).