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Hello and thanks for taking your time to help.

On the picture below you can see the 40244 that I have issues with.
While it is clear to me what most symbols mean, I am confused about the "20".
Some insight on it would be great. (hopefully it is not just number of pins...)

40244

EDIT: looking more at it, it looks more like an "O" than a "0"

EDIT2: So far it seems to me, that its meaning is that 2 Pins/Inputs are responsible for each Output (2 O(utput))

Final EDIT: Thanks for @Finbarr ´s Answer, makes the most sense to me.

enter image description here

Pseudoflask
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  • Here you have only half of the component. On your schematic you should have maybe two of them. So based on this, the "2" could says "there is two" and the "0" means "it's the first one (upper-side of the componnent). Is there a "2 1" ? – Tagadac Mar 02 '17 at 11:10
  • Unfortunatly the second part does have the same symbols on it – Pseudoflask Mar 02 '17 at 11:11
  • Is it possibly a grid reference? Row two, column O position? – Whit3rd Mar 02 '17 at 11:19
  • Found this component, maybe the "2" is linked with the "9" and "10" : http://www.ti.com/lit/ds/symlink/sn74als259.pdf – Tagadac Mar 02 '17 at 11:21
  • According to this document : http://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf the "9", is linked with the "Z9" which it says "imposes Z state to all 9". So maybe like @Pseudoflask says it is not a "0" (zero) but "O". And maybe according to an holder/newer standard (is your symbol an hold symbol from an hold schem ?) it says something about the way the things are linked together inside the component. – Tagadac Mar 02 '17 at 11:48
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    Thanks alot @Tagadac considering that information and taking a look in the schematics in the datasheet of the 40244 that indeed makes sense. "2" Pins(Inputs) are responsible for each "O"utput – Pseudoflask Mar 02 '17 at 12:09
  • Just count the pins. The device has 20 pins its obvious that the 20 stands for 20 pins ! – Coolbreaker Mar 02 '17 at 10:54
  • Pin 20 is positive supply voltage and in addition pin numbers are already located outside the symbol (it can't be pin 2 and pin 20 at the same time). So obviously "2O" doesn't mean pin #20. – Curd Mar 02 '17 at 10:58
  • Nop ! http://www.farnell.com/datasheets/71882.pdf As pin 2 is an input and pin 20 is VDD ! – Tagadac Mar 02 '17 at 10:59
  • actually looking more at it, it actually looks more like an "o" instead of a "0" – Pseudoflask Mar 02 '17 at 11:10
  • Maybe 2-and-Onwards to avoid the repetition of the symbols in the following boxes. – Andrew Morton Mar 02 '17 at 14:06

2 Answers2

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It means....

Nothing. The symbol is entirely correct without it. The right arrow symbol denotes a function with an enhanced level of output (e.g. buffer or line driver) flowing from left to right and the down arrow symbol denotes a 3-state output. The upper rectangle denotes a control block associated with the lower rectangles, which in this case simply consists of an enable signal. There is no need to mark the inputs with anything unless they are controlled by different elements of the top block (for instance, if you combined the two separate halves of the device into one symbol) and, even then, you'd use a D not an O.

I say the symbol is correct without it, actually it isn't really. The enable line should EITHER have a circle to show it's inverted OR a bar over the name but not both.

I suspect someone entered the symbol definition incorrectly into the CAD system ages ago and people, like you, have been scratching their heads ever since. Texas used to use these sorts of symbols in their data books but I think they've dropped them now - probably because to understand them you had to pay for the relevant ANSI/IEEE/IEC standards and nobody ever did.

Finbarr
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  • Thanks for the comprehensive answer. Researched alot and there is literally no reference to be found anywhere else. So beside interpretations I had nothing to go on. – Pseudoflask Mar 02 '17 at 13:58
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    You're welcome. It was a brave effort to standardise logic symbols but I think they bit off more than they could chew and for anything more than the simplest of functions it became a bit of an incomprehensible mess. I suspect that if you dig around enough manufacturer data sheets you'll find the correct symbol. – Finbarr Mar 02 '17 at 14:04
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Short answer is "Beats me."

If "2O" or "20" has a standard meaning it doesn't come jumping out on reading TI's overview of "IEEE Standard 91-1984" (since renumbered as an IEC standard). It doesn't add anything to the symbol - if not there, it wouldn't be missed. It certainly isn't the number of pins, and doesn't mean that "'2' Pins(Inputs) are responsible for each 'O'utput" since the enable input is understood to control all the data sections: it appears in the common control block. If a grid reference was to appear anywhere, having it next to a data input would be a bad choice.

What's missing from the symbol is the hysteresis qualifier that all the inputs, including Enable, should have. Guessing that "2O" is a company-specific hysteresis qualifier wouldn't be out of the question, except that there's nothing next to the Enable.