4
\$\begingroup\$

I'm still just beginning my adventure into electronics and IC chips and datasheets have me confused so I'm going to ask a series of beginner questions will help me and hopefully others as well.

There are many different IC and IC manufactures out there. Specifically for the 74 line, are these chips standard across the different manufacturers? If not, what are generally the differences between them? Will it matter if I mix and match different ICs from different manufactures?

Datasheets, for some reason these tend to be horribly thought out and rather difficult for a beginner like me to decipher (I've noticed TI is notorious for this, giving abbreviations to all their pins without any explanation. What the heck is OE?). Is there a company (assuming that all chips are standard between different manufacturers) that provides clear and concise datasheets for all of the 74 IC chip line?

\$\endgroup\$
  • 1
    \$\begingroup\$ Are you sure the datasheet doesn't explain what "OE" means? There's almost always a list of the pins and their functions. \$\endgroup\$ – endolith Apr 22 '11 at 13:36
7
\$\begingroup\$

OE is Output Enable. :-)

Logic ICs with the same number have the same functionality and pinout across manufacturers. A 74xx32 is always a quad 2-input OR gate. The technology used may be different though; a 74LS32 is low-power Schottky, while a 74HC32 is high speed CMOS. These families have their particular properties, which you'll find in a "Logic Family Guide".
Sometimes there are small differences in the details. I remember a Schmitt-Trigger inverter I once use for an oscillator, which generated a complete different frequency when using make Y instead of X. Reason: different trigger levels, these are not standardized.

I never realized this before, but you're right: the datasheets have many terms and abbreviations which are not clearly explained. At least not in the datasheet. The datasheet often refers to the Logic Family Guide, which contains information concerning the whole series. That way they avoid datasheets becoming twice as long because they contain all this information time and again.

edit
I checked with a few datasheets from different manufacturers, and I must say, it might have been worse. For many parameters there are tables with a column "symbol", and next to it a column "parameter", which describes it briefly. The "OE" appears as abbreviation in truth tables, but for what it stands for you'll have to read the ICs description.


See also this answer about datasheets.

\$\endgroup\$
  • \$\begingroup\$ So far I've found that NXP is the best by far, or at theirs doesn't look like it was scanned and PDFed like TI's \$\endgroup\$ – Faken Apr 22 '11 at 12:24
  • \$\begingroup\$ @Faken - I don't see anything wrong with TI's documents, in fact I still own a 1980 copy of "The TTL Data Book for Design Engineers", which at the time was a standard. \$\endgroup\$ – stevenvh Apr 22 '11 at 12:53
4
\$\begingroup\$

Most chips of a certain type will have nearly the same specifications. You have to be careful how you define 'type' here though; those letters in the middle (e.g. LS, HCT, and so on) will result in different speeds, current capability, etc.

Better data sheets will have a 'pin description' section, which will tell you what things like 'OE' actually do. For example, OE is almost always 'output enable'.

\$\endgroup\$
1
\$\begingroup\$

Typically, one manufacturer will develop a part and offer it for sale. If that part is successful, other manufacturers will develop substitute parts to match, either because there's a market-wide demand for the product, and/or because the original manufacturer licensed the design to others to assure a second-source supply of the part.

In most cases, the secondary producers will use similar technologies to achieve similar performance specs.

It's the technology that generally drives the performance of the part. That is why for the smaller IC's (74xx and 40xx), there's a "family" of parts.

The 74 series actually have many different families - the original 7400 family, the 74S, 74LS, 74F, 74HC, 74HCT, and so on (look at the Wikipedia entry on the 7400 series) -- some of the technologies within the overall 7400-series varients are quite different from each other, and the main reason why they're named 74xx is because the naming of the devices are kept the same for the same functionality. So you know that a 74(foo)00 is a quad-NAND, 74(foo)373 is an octal transparent latch, and so on.

As stevenvh pointed out, there's usually a "family guide". Actually, there used to be dataBOOKS that had the family technology information in the front, followed by the per-device data. As these big encyclopedic books have fallen out of favor, you now mostly see individual datasheets, and a separate guide to the technology.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.