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74HC/HCT/LS ????????????????????????????
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| Lyos Gemini Norezel | Post subject: 74HC/HCT/LS ???????????????????????????? Posted: Mon Jan 19, 2004 9:20 pm | |
| Joined: Sun Dec 28, 2003 11:55 amPosts: 54 | | Hello... need some help here... are the LS/HC/and HCT series IC's compatible? Ie., is a 74LS139 compatible with the 74HCT139? Any info/help would be much appreiciated.Thanks.Lyos Gemini Norezel _________________Mundus Vult Decipi et Decipiatur | |
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| orac | | Post subject: Posted: Tue Jan 20, 2004 12:38 am | |
| Joined: Sat Aug 31, 2002 12:33 pmPosts: 64Location: USA | | Hi Everyone, You can learn the difference by going to the "logic" portion of the major chip manufacturers web-sites (that still sell logic chips). There, look through the application notes for an overview of different logic families. They will have it! Try Texas Instruments Fairchild ST Toshiba among others. Cheers, Paul | |
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| GARTHWILSON | | Post subject: Posted: Tue Jan 20, 2004 1:58 am | |
| Joined: Fri Aug 30, 2002 1:09 amPosts: 8557Location: Southern California | | I know the search here doesn't work very well, but the forum archives are kept for a good reason. Look at viewtopic.php?p=909 or go to forum index --> hardware --> 6522 vs. WDC 65c22. You'll find lots of information and enough informative ap. note references to keep you busy for a week, all relevant to your exact question. Have fun! _________________http://WilsonMinesCo.com/ lots of 6502 resourcesThe "second front page" is http://wilsonminesco.com/links.html .What's an additional VIA among friends, anyhow? Last edited by GARTHWILSON on Tue Jan 30, 2007 8:55 pm, edited 1 time in total. | |
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| Nightmaretony | | Post subject: Posted: Wed Jan 21, 2004 7:37 am | |
| Joined: Fri Jun 27, 2003 8:12 amPosts: 618Location: Meadowbrook | | At salower speeds, all are ocmpatible to a point. The HC series being a CMOS does NOT have the larger fanout of the LS and S series. For the real wierd families, I have absolutely no clue. But in general, if you are driving very little load at slower speed, they should all work. As a rule of tyhumb, I go by: LS: general purpose HC: low current CMOS, TTL compatible S high speed _________________"My biggest dream in life? Building black plywood Habitrails" | |
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| orac | | Post subject: Posted: Wed Jan 21, 2004 2:37 pm | |
| Joined: Sat Aug 31, 2002 12:33 pmPosts: 64Location: USA | | Hi Everyone, There is a lot to this subject so I again suggest that you read the APP notes from the manufacturers. For example: 0) HC is slower than LS. 1) HC is not TTL compatible (HCT is though, but still slower). Cheers, Paul | |
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| Lyos Gemini Norezel | | Post subject: Posted: Wed Jan 21, 2004 3:34 pm | |
| Joined: Sun Dec 28, 2003 11:55 amPosts: 54 | | Thanks for the info/links... I appreiciate the help. Lyos Gemini Norezel _________________Mundus Vult Decipi et Decipiatur | |
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| GARTHWILSON | | Post subject: Posted: Wed Jan 21, 2004 6:35 pm | |
| Joined: Fri Aug 30, 2002 1:09 amPosts: 8557Location: Southern California | | > The HC series being a CMOS does NOT have the larger fanout of the LS and S series. For the 74xx139 you specifically asked about, my 1988 National Semiconductor data book specifically says of the 74HC139 (not even HCT139): "The decoder's outputs can drive 10 low power Schottky TTL equivalent loads" (their exact wording). The fanout given for LS is 20. So although the HC-to-LS fanout is less, it's still probably more than enough for what most people on this forum want to do. > 0) HC is slower than LS. I've heard this many times; but according to my National Semiconductor and Fairchild databooks, HC is generally a little faster-- not in every single case, but usually. They make a point of that in the ap. notes as well. > 1) HC is not TTL compatible (HCT is though, but still slower). It's not 100% compatible, but they can be used with each other under certain conditions. The 65 family's inputs are all geared toward TTL voltage thresholds; but when everything in the circuit is some kind of MOS (NMOS, CMOS, etc.), HC works perfectly fine because all the 1's will be driven right near 5V and the 0's right near ground anyway, so the "turnover" point becomes irrelevant. For many years I've used HC almost exclusively with the 65 family, with no problems. Putting in the occasional LS part until I could get the HC I originally wanted has not been a problem functionally, although the LS part takes a lot more power supply current. Now I mostly use 74AC or ACT. 74ACT is both compatible and much faster than either HC or LS. Again, see the many ap. notes with links in the 6522 v. WDC 65c22 forum subject. | |
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| orac | | Post subject: Posted: Wed Jan 21, 2004 10:17 pm | |
| Joined: Sat Aug 31, 2002 12:33 pmPosts: 64Location: USA | | Hi Everyone, Its all in the details..... Here are two data sheets from Ti. http://focus.ti.com/lit/ds/symlink/sn74ls541.pdf http://focus.ti.com/lit/ds/symlink/sn74hc541.pdf 74LS540 ====== Propagation delay typical = 9 nsec Propagation delay max = 15 nsec 74HC540 ====== Propagation delay typical = 9 nsec Propagation delay max = 19-22 nsec Remember some chips fall into the "max" bin when they are shipped. Not all are "typical". Also, LS cannot drive HC without pull-ups! HC can drive LS with no problem. Maybe this is what Garth was thinking. Cheers, Paul | |
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| bogax | | Post subject: Posted: Wed Jan 21, 2004 11:33 pm | |
| Joined: Tue Nov 18, 2003 8:41 pmPosts: 250 | | "Also, LS cannot drive HC without pull-ups!" Not strictly true. There are two problems. One is that the voltages are different. A TTL input is spec'd to see anything over ~2V (1.8V actually, IIRC) as a logic high, and the outputs are spec'd to pull up to a minimum ~2.4V (actually 2.45V IIRC) CMOS is usually very symetrical and has a threshold of close to 1/2 VCC, ie 2.5V, so the TTL spec. doesn't gaurentee what CMOS "wants" for a high, voltage-wise. Never the less the TTL high output voltage is usually in the 3-4V range (I think 3.5V usually given as typical) and it's seldom a problem. (In my experience) The other problem is that TTL doesn't source much current, so even if it can attain a high enough voltage, it may not do it very fast (it may not be able to charge the CMOS input capacitance quickly). And that voltage may not be very high compared to what the CMOS would "like". Both of which can slowdown the CMOS the TTL is driving. Worse, the slow transitions can cause problems like not clocking or erratic behavior because of a minimum clock speed spec. (not fast enough for some AC coupled internal CMOS thing or the CMOS oscillating as the input lingers near the threshold). And it'll be more susceptible to noise (especially as it passes though the threshold). | |
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| GARTHWILSON | | Post subject: Posted: Thu Jan 22, 2004 6:58 am | |
| Joined: Fri Aug 30, 2002 1:09 amPosts: 8557Location: Southern California | | > 74LS540> ====== > Propagation delay typical = 9 nsec > Propagation delay max = 15 nsec > > 74HC540 > ====== > Propagation delay typical = 9 nsec > Propagation delay max = 19-22 nsec > > Remember some chips fall into the "max" bin when they are shipped. > Not all are "typical".I had some trouble with the TI website so I tried to look at some other manufacturers and was a little surprised to find that none of the ones I thought of checking supported LS anymore. However, going back to my own National Semiconductor paper data books, the 74xx139 that Lyos originally mentioned had the same worst-case propagation delays in LS as in HC at 25 deg C and 15pF load. In the case of the 74xx00, LS's typ/max is 10/15ns compared to HC's 8/15ns, and for the 74xx04, LS's numbers were 10/15ns compared to HC's 7/13ns, again all under the same conditions. I said earlier that HC was generally (not universally) slightly faster than LS, but some parts will go one way and others will go the other way. Now I'm finding the same thing in Fairchild's ap. note AN-368: "HC and HCT speeds are not identical to LS-TTL. Some delays will be faster and some slightly slower. This is due to inherent differences in designing with CMOS versus bipolar logic. For an average system implemented in HC or LS-TTL, the same overall performance will result. On an individual part basis, some speeds will differ."> Also, LS cannot drive HC without pull-ups!Fairchild's AN368 says in the fifth paragraph on the first page, "It should be noted that in an actual application the TTL output will pull up probably to about Vcc minus two diode voltages [about 3.7V --GW], and HC will accept voltages as low as 3V as a valid one level so that in almost all cases there is no problem driving HC with TTL." They do go on to say however that the situation can be improved with a pull-up resistor, although I never found where they recommended a value.I've driven HC with LS many times without pull-ups and never had a problem; but if, as the ap. note says, some HC may not be in solid "1" territory until you get to 3.5V and some LS won't pull up much higher than that, it is understandable why they say "in almost all cases there is no problem" but also say it is not guaranteed, which partly supports Paul's point. _________________http://WilsonMinesCo.com/ lots of 6502 resourcesThe "second front page" is http://wilsonminesco.com/links.html .What's an additional VIA among friends, anyhow? | |
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| orac | | Post subject: Posted: Thu Jan 22, 2004 10:24 pm | |
| Joined: Sat Aug 31, 2002 12:33 pmPosts: 64Location: USA | | Hi Everyone, Good discussion. Thanks for the update. Cheers, Paul | |
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| fachat | | Post subject: Re: 74HC/HCT/LS ????????????????????????????Posted: Sat Apr 28, 2012 12:21 pm | |
| Joined: Tue Jul 05, 2005 7:08 pmPosts: 1043Location: near Heidelberg, Germany | | I often use the 74ALS family as a modern replacement of the 74LS. It's faster than the 74HCT (4ns prop. delay vs. 9ns), and still draws less power than 74LS, but now as little as the HCT.André _________________Author of the GeckOS multitasking operating system, the usb65 stack, designer of the Micro-PET and many more 6502 content: http://6502.org/users/andre/ | |
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| GARTHWILSON | | Post subject: Re: 74HC/HCT/LS ????????????????????????????Posted: Sat Apr 28, 2012 7:24 pm | |
| Joined: Fri Aug 30, 2002 1:09 amPosts: 8557Location: Southern California | | My National Semiconductor (now Fairchild) data book says the 74ALS00 and '04 max Pd is 11ns L->H @ 5V, 25°C. The output drive current for pulling down is very strong at 30mA min, but pulling up it's very anemic at -0.4mA at Vcc-2. Input load is lighter than LS. _________________http://WilsonMinesCo.com/ lots of 6502 resourcesThe "second front page" is http://wilsonminesco.com/links.html .What's an additional VIA among friends, anyhow? | |
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| BigDumbDinosaur | | Post subject: Re: 74HC/HCT/LSPosted: Sun Apr 29, 2012 6:04 pm | |
| Joined: Thu May 28, 2009 9:46 pmPosts: 8541Location: Midwestern USA | | Here's a good site that lists chip family comparisons. One family that the site doesn't mention is the 74ABT series, which is often used in bus driver chips, such as the 74ABT541. The 74ABT family is very fast (single digit nanosecond performance) and has high fanout. Their outputs, however, at TTL, not CMOS.The families I recommend for new designs are 74AC and 74HC. The former is very fast, but also may give rise to noise and ringing problems if physical construction isn't right. 74HC is more tolerant of sloppy construction. _________________x86? We ain't got no x86. We don't NEED no stinking x86! Last edited by BigDumbDinosaur on Sun Jan 31, 2021 6:59 pm, edited 1 time in total. | |
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| GARTHWILSON | | Post subject: Re: 74HC/HCT/LS ????????????????????????????Posted: Sun Apr 29, 2012 9:52 pm | |
| Joined: Fri Aug 30, 2002 1:09 amPosts: 8557Location: Southern California | | Yes, I sure wish more parts were available in 74ABT. _________________http://WilsonMinesCo.com/ lots of 6502 resourcesThe "second front page" is http://wilsonminesco.com/links.html .What's an additional VIA among friends, anyhow? | |
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