Logic levels specification syntax

[tluxon]

First, I'm an ME, not an EE, so my question is probably going to seem pretty lame. I have a question about the syntax of a note I found on a number of our specification drawings. The note says,

"Logic levels of digital signals is ±5 VDC."

Now, the "is" confuses me - it seems like it should be "are" for proper english. Secondly, the "±5" has me confused too, since I thought voltages on a logic chip were always positive, with a low voltage for "low" and a high voltage for "high".

Can anybody shed some light on what this note might mean or what it "should" say instead?

Thanks,

Tim

 

[Lewish]

OK, my $0.02 worth. Having been an EE for 30+ years, my response to your question is:

"It is a worthless ambiguous statement".

In other words, it has no usefulness. Logic is normally single ended positive supply, unless you are using ECL, etc., and typically is +5V. But, I have done +15V logic in very noisy environments. But, I have yet to do ±5V.

I hope this helps.

 

[synchron]

It could be stated like this depending on how "GND" is defined in the particular ckt. Some communication protocols (i.e. RS-232) state +5 - 12VDC = logic High
0 - -12VDC = Logic low.