74lsXXX vs 74XXX chip famies? - Page 1
Forum section: electronics / projects

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: September 01, 2024, 11:25:09 pm
content: I bought a bunch of dip tubes and plugs, so ive been sorting and labeling my massive collection of chips.. how fun. Anyways i have a lot of old parts, while sorting my logic gates i found some chips like thisIm assuming this is just a 74xx121, but is it the same as a 74ls121? From a quick search its TTL, but can i count on 74 being the same speed and pinout as 74ls?

author: wraper
author_rank: Unknown
timestamp: September 01, 2024, 11:30:49 pm
content: Logically it's the same as 74LS, it's TTL too but electrically it isn't the same. Much higher current consumption, has higher input current.

author: Kim Christensen
author_rank: Super Contributor
timestamp: September 01, 2024, 11:46:53 pm
content: The 74LSxx is faster and draws less power than the plain old 74xx series. Not much use for these today except for repairing vintage equipment and nostalgia.Good summary on Wiki.

author: tooki
author_rank: Super Contributor
timestamp: September 01, 2024, 11:50:40 pm
content: Quote from: rwgast_lowlevellogicdesin on September 01, 2024, 11:25:09 pmPinout: very likely yes. (I’ve heard there are a few exceptions, but normally they are pinout-identical.)Speed: absolutely not. That varies by logic family.Seehttps://www.ti.com/lit/sg/sdyu001ab/sdyu001ab.pdf

author: Zero999
author_rank: Super Contributor
timestamp: September 02, 2024, 08:57:15 am
content: I wouldn't bother stocking plain old 74 or even 74LS. The exception being the74LS06, which can drive 30V loads up to 40mA. My advice is sell them on, unless you have a specific need for them.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 02, 2024, 09:10:25 am
content: I would take that as an equivalent for SN74121, TTL monostable. N stands for Normal TTL, so not LS TTL.https://www.ti.com/lit/ds/symlink/sn74121.pdfA brief list with main characteristics for each logic family by TI:Logic Guidehttps://www.ti.com/lit/sg/sdyu001ab/sdyu001ab.pdf

author: David Hess
author_rank: Super Contributor
timestamp: September 02, 2024, 11:29:02 am
content: Quote from: rwgast_lowlevellogicdesin on September 01, 2024, 11:25:09 pmFunctionally the 74121 would be the same as a 74LS121, and usually TTL and LS TTL may be interchanged. However I am not sure the 74LS121 ever existed because it is not listed in The TTL Data Book, although the 74L121 is.In general, LS TTL is the same speed as TTL, but at like 1/5th the power level. Usually they are interchangeable, but not always. LS TTL and TTL have different fan-in and fan-out requirements.

author: coppice
author_rank: Super Contributor
timestamp: September 02, 2024, 11:36:44 am
content: Quote from: Kim Christensen on September 01, 2024, 11:46:53 pmLS is usually in the same ballpark for speed as a similar non LS part. LS went for similar speed, lower power. S went for similar power, higher speed. Sometimes they went overboard with the S part, and it takes considerably more power.

author: tooki
author_rank: Super Contributor
timestamp: September 02, 2024, 02:35:00 pm
content: Quote from: RoGeorge on September 02, 2024, 09:10:25 amNo, N does not stand for "Normal TTL"!Original TTL chips simply have no letters between the 74 and the rest of the number (e.g. 74xxx). Every other logic family inserts letters there (e.g. 74LSxxx).The N on a 74121N means plastic DIP package, in TI logic chips.The SN prefix is TI's prefix for standard logic, and is short for "semiconductor network". (Source:https://archive.org/details/bitsavers_tiTexasInsSeriesMorrisDesigningWithTTLIntegratedCi_11927910/page/n25/mode/2up)

author: TimFox
author_rank: Super Contributor
timestamp: September 02, 2024, 04:09:01 pm
content: Comparing simpler logic gates, such as the 7400 and 74LS00 quad NAND gates:In the older 7400 "standard" TTL circuit, the input device is a multiple-emitter NPN transistor (hence the name transistor-transistor logic).There were also 74L00 (low-power variant of 7400) and 74H00 (high-power faster variant) true TTL devices.The 74S00 high-speed gate uses NPN transistors with Schottky junctions to reduce stored-charge switching delays, including the input multiple-emitter NPN stage.The later 74LS00 has the same pinout and function, but the input stage is actually DTL (diode-transistor logic) using Schottky diodes at the input, and voltage levels compatible with the 7400 but different current levels.The internal NPN transistors have Schottky junctions to reduce stored charge.Other variations include the 74F00 from Fairchild that had different trade-offs between speed and power.When connecting one series to another, there is usually no problem with the voltage levels for logic 1 and 0, but care must be taken that the total current drawn by the loads (especially in logic 0 low state) must be within the spec for the driver in its low state, at the specified logic voltage level. For example, a 7400 can drive more 74LS00s (in parallel) than a 74LS00 can drive 7400s.

author: coppice
author_rank: Super Contributor
timestamp: September 02, 2024, 04:20:01 pm
content: Quote from: TimFox on September 02, 2024, 04:09:01 pmYou missed H, ALS and AS if you want to list the full set.

author: TimFox
author_rank: Super Contributor
timestamp: September 02, 2024, 04:30:57 pm
content: I mentioned "H", merely a high-current variation on 7400.I did not include the later CMOS series that were pin-compatible with the 7400 TTL series but have different electrical characteristics that can be compatible with 7400.

author: David Hess
author_rank: Super Contributor
timestamp: September 02, 2024, 04:32:54 pm
content: Quote from: TimFox on September 02, 2024, 04:09:01 pmFairchild F TTL was FAST or Fast Advanced Schottky TTL, with similar performance to AS TTL or Advanced Schottky TTL.Fast Advanced Schottky TTL had amazing performance which was limited by DIP packages and even small outline packages because the corner connections of ground and power had too much inductance. It had about the power requirements of LS, but was faster than schottky TTL, and had excellent drive. Unfortunately not many functions were transferred and it never became as popular as LS, which it could almost always replace.

author: coppice
author_rank: Super Contributor
timestamp: September 02, 2024, 04:49:26 pm
content: Quote from: David Hess on September 02, 2024, 04:32:54 pmAlthough F, AS and ALS never existed as full lines of parts, like the earlier families, they did make a big difference. Vendors focussed on the parts customers said were holding them back, like latches and buffers, and they sold well. Not every part in a system needs to work at blistering speed.There was a push to produce variants with the power pins in better places. I'm not sure if many of those actually went out the door.

author: David Hess
author_rank: Super Contributor
timestamp: September 02, 2024, 06:17:42 pm
content: Quote from: coppice on September 02, 2024, 04:49:26 pmLower inductance power and ground pin placement is more important for CMOS where the rise and fall times are faster. Bipolar logic families had an advantage with slower slew rates for the same propagation delay, which I suspect was because at a given current, bipolar transistors have higher transconductance than MOSFETs.Center aligned power and ground became available after FAST TTL for both CMOS and bipolar, but I do not remember if FAST or AS ever got that.

author: CaptDon
author_rank: Super Contributor
timestamp: September 03, 2024, 03:16:15 pm
content: What a laugh "N stands for normal", where in the hell did he get that from??? The reply N stands for the packaging type is correct. As for the 'LS' verses non-LS and L versions of the one shot devices there is a huge difference in the timing component values needed for a specific pulse width. This is true of the 74121, 122 and 123 devices. There is also a difference in the minimum and maximum pulse widths as well as the high and low value limits of the timing components themselves. 74XXX and 74LSXXX parts are valuable for experimenting and breadboarding. the 74ACTXXX series is so incredibly fast that they seldom work correctly on a breadboard. You will find these older parts still sell very well on Ebay, particularly when they are New Old Stock in the sleeves.

author: CaptDon
author_rank: Super Contributor
timestamp: September 03, 2024, 03:27:49 pm
content: The militarized 5400 54XX series had a lot of parts with 'centered' power pins making them hard to find for repairs today. Although the function of the chip 7400 vs. 5400, 7410 vs. 5410 etc. were usually the same the pinout was often different and the specs were different. One example I seem to recall is a 7400 was spec'd 4.75 to 5.25 volts VCC where the 5400 stuff was 4.5 to 5.5 volts VCC.

author: coppice
author_rank: Super Contributor
timestamp: September 03, 2024, 04:40:19 pm
content: Quote from: CaptDon on September 03, 2024, 03:27:49 pmThe 5400 and the related military DIP parts were pin compatible with the 74xx DIP parts. We used the 74xx parts for all our military development, and eventually the military parts went into the final qualification testing prototypes and production units. Some people confuse 54xx with military. They aren't the same. 74xx was commercial temperature range. 64xx was industrial temperature range, although you rarely saw them. 54xx was military temperature range, normally in ceramic packages. As you noted, some of the timings and other parameters were different for the various versions, but if your design worked with 74xx parts it would generally be OK with the 54xx parts.Above the 54xx parts were the actual military parts, where each individual part went through extensive qualification, and cost a fortune. They were distinguished by the alpha part of the device name. The 54xx, 64xx, and 74xx naming is similar to the 1xx, 2xx and 3xx nomenclature that National and others used for similar analogue parts in different temperature ranges.Things like the flat pack versions of 54xx parts often had a different pinout from the DIP ones. Is that what you are talking about?

author: tooki
author_rank: Super Contributor
timestamp: September 03, 2024, 07:22:14 pm
content: Quote from: coppice on September 02, 2024, 04:20:01 pmAll of those together don't even come close to being the full list of 74-series logic families.

author: coppice
author_rank: Super Contributor
timestamp: September 03, 2024, 07:26:56 pm
content: Quote from: tooki on September 03, 2024, 07:22:14 pmIts not all the 74 series, as someone else noted, but I think its all the bipolar ones. There were also related families of 74 compatible devices, like the Am25xx and Am29xx series of Schottky TTL chips, various things from Signetics (e.g. early forms of programmable logic), and others.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 03, 2024, 08:22:09 pm
content: Showing the frequency/voltage curves for a few different 7400 gates arranged into a ring oscillator:https://www.eevblog.com/forum/projects/waveforms-in-a-74ls04-ring-oscillator/msg645164/#msg645164

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 03, 2024, 10:04:58 pm
content: I also recall those 74xx TTL devices with nostalgia, as I learned the basic logic circuit concepts with them.Nowadays if I would want to use them, for whatever the reason, I would choose the 74HCxx or 74HCTxx devices instead, which have improved electrical characteristics.

author: tggzzz
author_rank: Super Contributor
timestamp: September 03, 2024, 10:34:13 pm
content: Quote from: schmitt trigger on September 03, 2024, 10:04:58 pmOr the 74LVC* devices. Small, fast, drive 50ohms, low inductance PSU leads.

author: David Hess
author_rank: Super Contributor
timestamp: September 03, 2024, 10:56:39 pm
content: J is the ceramic DIP package, N is the plastic DIP package, and W is a ceramic flat package, at least from Texas Instruments. The 74 series was available in the plastic and ceramic DIP packages, and the 54 series was available in the ceramic DIP and ceramic flat packages.Only the ceramic flat package had center located ground and power pins, and I think it was only for layout rather than performance reasons. Later faster logic families like AC used center located ground and power pins for performance reasons.Quote from: schmitt trigger on September 03, 2024, 10:04:58 pmI prefer the HC and HCT families as well, but most of the old test instruments that I repair or improve use the bipolar TTL families. For mixed signal stuff, the higher voltage 4000 and 74C series are more useful even though they are slow.Quote from: tggzzz on September 03, 2024, 10:34:13 pmI think LVC is the fastest since it still supports 5 volt power, and it would be my first choice unless the lower voltage stuff is faster.

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 03, 2024, 11:37:00 pm
content: Quote from: schmitt trigger on September 03, 2024, 10:04:58 pmYou should change your username if you don't add 74HCS into your preferred choice

author: tggzzz
author_rank: Super Contributor
timestamp: September 03, 2024, 11:47:53 pm
content: Quote from: David Hess on September 03, 2024, 10:56:39 pm(Some LVC is apparently only 3.3V)This kind of discussion is a good example of how TAoE can save a lot of peoples' own time. If readers of this thread haven't got a copy...get one!From TaOE 3rd edition Section 10.2.3 CMOS and bipolar (“TTL”) characteristics"..."...Among them, the LVC and 7SZ families are nice, with their 5 V tolerant inputs and good supply voltage ranges (1.8–3.3 V and 1.8–5 V). For operation at 5 V the AHC(T), VHC(T), or LV families are also good choices; their inputs are 5 V tolerant regardless of supply voltage (which can be 2.5–5 V). These parts are available only in surface-mount packages; if you want DIP through-hole parts for ease of breadboarding, use HC(T) or AC(T)."