Hi Attila! Let me answer this first, as you appear to be need better context:
Attila Kinali wrote: > On Sun, 11 Nov 2007 10:04:22 -0600 > Terry Hancock <[EMAIL PROTECTED]> wrote: >>-- which >>is (AFAIK) all the Verilog will encode anyway. > > Where does Verilog come into the game with 74s?> A little learning project some OGP folks started: http://wiki.opengraphics.org/tiki-index.php?page=HDL_Resources (Scroll down to the bottom). They're implementing 7400 series in Verilog/HDL. The purpose of the datasheets is to know what to implement. >>JB suggested off-list that I should mention that inserted letters in >>7400-series chips are usually not significant for our purposes. The point here, is that a datasheet for a 74HC138 will show the same logic as a 74138, etc. Since the differences are in technologies rather than logical design and pinouts, they really don't matter -- Verilog does not (I think) model the analog aspects of chip design that the implementation technology determines. > Little correction here, HC stands for High Speed CMOS (in contrast Oops. Thanks. Just pulling examples from memory. > The incompatibilities are in the voltage levels for high/low only. > CMOS uses level relative to Vcc, while TTL has fixed (and incompatible > positioned) levels. Though nothing that could not be fixed with a simple > pull up resistor. I was under the impression that a TTL input would suck down a CMOS output due to the power consumption, damaging the CMOS chip. TTL is relatively low impedence, so it flows current whenever it is on (hence the high power dissipation -- TTL chips get *hot*), while the CMOS is high impedence, so it doesn't flow much current except during switching. (Or so has been my limited understanding -- this fits with my experience of discrete bipolar and FET transistors, though). Anyway, it used to be a rule that you never used them together that way. But that was with early versions of the chips -- later on, there were TTLs that used less current and CMOS that could tolerate more, and so you had devices that could work together. But I've long since lost track what was what and what the technology is like today. I just know there's a lot of alphabet soup that gets stuck into the labels, but they're conceptually the same chips. >>Letters at the beginning are probably manufacturer codes (I'm not >>certain, though). > > Yes, they are. Leaving me to wonder why "SN" means "Texas Instruments", but nevermind. ;-) >>Letters at the end usually indicate package codes. When the 7400s first >>came out, they were all in standard 0.3" wide, 0.1" pin-pitch >>through-hole DIP packages. But many of these are for various "small >>outline" / "surface mount" packages which are a lot more compact. I'm >>discovering that there is a bewildering array of these, though. > > Never trust the package codes of any device without samples. > Especially not 74s and even less if your distributor uses > "equivalent" types from a different manufacturer. > > Oh yes, and check the codes printed on the packages that > you actually got the right chips. For some reason a lot > of distributors seem to have troubles to label 74s in > small SMD packages correctly. This may be great advice if you're buying chips, but is drifting further and further off topic for implementing Verilog examples. :-) >>Anyway, they should still have the same arrangement of pins. > > Nope. Only if they are still 14 pin. Okay, I'll grant that -- we need to check for a DIP pin arrangement. > But these days a lot of > the chips are single gates, which have a pseudo standard > (ie most use the same pinout, but not all). But why would they use 7400 labels for those at all? That's just evil. > (side note: most of the 74s with higher pin counts and > more complex functionality were replaced by CPLDs and FPGAs > and thus died out) Anyway, all the datasheets I've pulled up by searching for 7400 series numbers (so far) have been compatible with the pinouts in my (C)1980 "The Master IC Cookbook", so I think we're pretty safe. Cheers, Terry -- Terry Hancock ([EMAIL PROTECTED]) Anansi Spaceworks http://www.AnansiSpaceworks.com _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
