Why all of the Logic Chips - Page 1
Forum section: electronics / beginners

author: wigman27
author_rank: Regular Contributor
timestamp: August 12, 2014, 12:16:34 pm
content: G'day again,A very open ended question, in a number of Dave's tear-downs (most actually), there are so many Logic chips in the boards, whether it be 74 or 4000 series or something totally different.I have done a few projects now and I use the processor and software to do most of my logic operations. Am I doing it wrong? should I be looking to include external logic in my projects? Is it required?My original idea I had was that processors have developed so quickly and are capable of much more now then when I guess these devices were designed, that you had to do quite a lot of logic operations outside of the processor to save memory? Am I on the right track at all or I have I just not come across a need for them yet or missed an opportunity to use them?ThanksLee

author: Simon
author_rank: Unknown
timestamp: August 12, 2014, 12:19:08 pm
content: Logic chips were used a lot in the past because there was no alternative and they were and can still be faster plus you can dedicate them to the task unlike most microcontrollers. Of course in my mind and with some of the work i do now I would consider logic gates possibly more resilient and safer is the application is safety critical and you don't want the risk that your software locks up.

author: wigman27
author_rank: Regular Contributor
timestamp: August 12, 2014, 12:30:35 pm
content: That's a fair call!So it was mainly to extend the reliability and usability and take logic operations outside the micro controller.It may be interesting to do a project that required some logic, I must confess I have used a very small amount of it in a project I didn't design but it would be good learning to try and use some hard logic. Any suggestions on a good project that would be good to use external logic?Thanks MateLee

author: bwat
author_rank: Frequent Contributor
timestamp: August 12, 2014, 12:40:08 pm
content: Quote from: wigman27 on August 12, 2014, 12:16:34 pmIf it works for you then you're not doing it wrong.Quote from: wigman27 on August 12, 2014, 12:16:34 pmA processor is just programmable logic. The CPU'sdatapathcontainsarithmetic and logic circuitsand maybe ashifter, andregisterswhich are configured by acontrol unit. Your software is used by the control unit to determine the configuration. So it really doesn't make much difference forsequential circuitsif it is done by a CPU or a dedicated circuit.

author: Simon
author_rank: Unknown
timestamp: August 12, 2014, 12:41:50 pm
content: if you wanted to do fancy sequencing lights or similar you could use logic, you could use a counter to generate a sequence of numbers from a clock signal that can be as slow as need be and you can then build a combination logic circuit that takes the number sequence and uses it to determine which combination of outputs to turn off or on.often you will connect two open collector outputs on a comparator together with a common pull up resistor, this automatically forms a NOR gate.

author: bwat
author_rank: Frequent Contributor
timestamp: August 12, 2014, 12:48:55 pm
content: Quote from: wigman27 on August 12, 2014, 12:30:35 pmDrop the microprocessor/microcontroller and build something only from logic gates. Simon gave you some examples. You could even build your own CPU. There's a wealth of info out there and plenty of free simulation tools so you wouldn't have to spend any money. There's also cheap FPGA boards out these if you wanted to see it in action for real.

author: amyk
author_rank: Super Contributor
timestamp: August 12, 2014, 01:22:16 pm
content: One advantage of custom logic is that it can be asynchronous and parallel, unlike a CPU which has to execute instructions to simulate that. Large numbers of discrete gates have been replaced by CPLDs and FPGAs (and GALs/PALs/etc. before that), but you'll still find small numbers of discrete gates in use in various devices.

author: Bukurat
author_rank: Regular Contributor
timestamp: August 12, 2014, 01:30:05 pm
content: A lot of early equipment used TTL or CMOS logic gates, counters, flip flops etc because that's all that was available at the time. LSI is a relative newcomer.I have boards produced in the 70's and 80's that are full of TTL.

author: dentaku
author_rank: Frequent Contributor
timestamp: August 12, 2014, 02:14:13 pm
content: Logic ICs are also still useful when you want to cut down on the number of pins used by your microcontroller. Shift Registers, multiplexers and even 7-segment drivers and Schmitt-trigger inverters are all useful even today.I like messing with 4000 series stuff because it's fun to experiment with but I doubt I would be using flipflops, gates, counters, and such if I actually wanted to get stuff done in the real world except for the simplest of applications.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 12, 2014, 08:30:05 pm
content: A typical example would be, a processor to handle all the intricate, sequential operations required for operation (scheduling functions, analyzing I/O, implementing communication protocols, etc.), then discrete logic to encode/decode bus signals to implement internal I/O registers which connect to real-time functions: ADC/DAC, timers, controllers, etc. The discrete logic, in turn, could potentially be quite intricate, and verbose if production quantities remain small enough not to justify implementing it in an ASIC (as most PC system boards got -- compare the original IBM PC-XT motherboard to late models and clones). The reason for all the logic is usually reliability and real-time performance: with cheap processors topping out at a few MIPS, it was impossible to route tens or hundreds of signals through one, in real time.These lessons should not go to waste today. Computation is cheap, but processors crash. Pointers get corrupted. Software is inevitably the buggiest part of the system, and suffers the worst from the Dunning-Kruger effect: Bad programmers never realize how many ways their program will fail -- it should be no wonder why software is so popular, eh? -- while good programmers are constantly aware of potential problems, and attempt to avoid them.Today, logic is cheap, when implemented in a programmable array. But beware anything that comes back to code: it's just as possible, in firmware as in software, to make something functionally equivalent to the goal, yet which fails dramatically under various edge cases (in the simulator; in real implementation; under variation of inputs and timing; temperature and manufacturing variations; etc.).Undoubtedly, the same is still true of old discrete designs, but the much more lengthy (and expensive) design procedure likely would've included better testing (including breadboarding and real test signals), which at least helps. There's also the problem of timer sequenced logic: something you can't synthesize from VHDL, but which both simplifies (when done right) and massively complicates (when applied carelessly) discrete logic designs. There have been many discrete designs that were un-maintainable due to their use of complex webs of timer circuits. This (besides the inability to synthesize it) is why timed logic is frowned upon today.Tim

author: tszaboo
author_rank: Super Contributor
timestamp: August 12, 2014, 08:58:07 pm
content: I felt really weird the first time when I had to use discrete logic. But after a while I find it that I'm using more and more. And surprisingly, most of the times when if is near analog circuits.Like I had a board which had the LEDs on the front panel, MCU on the other side, precision analog in between. To keep the nosie down I had to buffer the signals driving the LEDs, because after several request not to, they still decided to make PWM for the LEDs.When the NOT gate was there, it was only microamps flowing next to the analog instead of ten miliamps. This was just one example.I've seen a (recently designed)power supply, where they had a CD4046 PLL to make the phase shift between phases. Genius usage. If you would go with a microcontorller, it just wouldn't fit on the board, because you need a power supply, level shifting back and forth... While the 4046 just run from the input ~12V.

author: tautech
author_rank: Super Contributor
timestamp: August 12, 2014, 10:15:35 pm
content: QuoteLogic still can be quite useful for simple designs and particularly in uPower applications.Done properly they are very reliable and cheap.The massive PCB's of yesteryear were pre LSI and SMD.Most of the 74 and 4000 series now can be had in SMD and that should ensure their survival for a few more decades.One must be aware of the families of these devices and their different supply and threshold requirements.A term that applied to strings of logic IC's, and not often seen these days, isglue logic, which describes how they are interfaced (stuck) together to provide the necessary result/output.

author: VK5RC
author_rank: Unknown
timestamp: August 13, 2014, 12:00:10 am
content: Who was it who said My favourite programming language is solder?

author: miguelvp
author_rank: Super Contributor
timestamp: August 13, 2014, 01:07:43 am
content: It was often used to address the CS_N when you had a lot of memory banks. I guess it does apply to other chip select pins for other things than memory. Like say you have several video processors sharing the same bus, you could select which one is currently active.

author: jeremy
author_rank: Super Contributor
timestamp: August 13, 2014, 01:35:06 am
content: Quote from: VK5RC on August 13, 2014, 12:00:10 ambunnie:http://www.bunniestudios.com/

author: Vgkid
author_rank: Super Contributor
timestamp: August 13, 2014, 02:12:49 am
content: Quote from: VK5RC on August 13, 2014, 12:00:10 amBob Pease. analog guru.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 13, 2014, 03:35:08 am
content: Quote from: NANDBlog on August 12, 2014, 08:58:07 pmExactly. Very often, you have an analog circuit which does everything it needs to, in and of itself: but you need control or management or status or fault detection to support that circuit. Well, all you need is a couple logic chips and you can implement all of that!And no, you wouldn't want to use an MCU here, even if you have one handy, because by "faults" I mean "mission critical", blowing stuff up, or zapping people, if it fails to trip. You can have software poking the registers that control it... in fact, that's the perfect place for it. But having it entirely in software, that's an invitation right there.It also allows you to build a bottom-basement absolutely stripped down minimal implementation of the project, which is otherwise fully functional and quite usable on its own: for example, a power supply with start/stop pushbuttons and control (volts/amps) pots. The digital implementation would simply provide these signals from logic pins and DACs hanging off an MCU.That way, the MCU gets to handle the things it's best at -- human or machine interface, driving a display, monitoring secondary conditions (like measuring voltages and temperatures -- rather than just tripping on a temp limit, say), things like that. If the MCU crashes, at worst, the interface goes dead and the process output gets stuck where it was. But you still have the big red "oh shit" button available to turn off the analog circuit, and it otherwise just keeps on doing whatever it's supposed to do.Tim

author: WarSim
author_rank: Frequent Contributor
timestamp: August 13, 2014, 05:38:20 am
content: I see nobody has used the reasons of serial vs parallel and synchronous and asynchronous. People seem to have exchanged these terms with digital and analog. Problem is they may be very descriptive. They are no as accurate as they should be for this topic.All types of computers had what is called analog and digital.Mechanical computers had both parallel resolvers and step stage processing.Electrical computers had both settle symbol resolution and set set processing.Then processing was diverged into what is called analog and RDL/DTL/TTL etc.Now that we have formulated new packaging in processors. uC, PLCC, FOGA, GAL etc. The old terms are being confused and readopted, to the point of being inaccurate.I believe the key is use what is required. Requirements are determined by specifications.Serial processing is a poor choice for very low latency applications. For example it will be some time before we will have DDS serial processors for XSHF.Discrete or packaged logic would be a poor choice for serialized tasks. For example the cost programable fabric or discrete logic cost more than equivalent serialized processors.Utilizing analog processing to accept and represent two or three state logic would not be cost effective. For example powering and controlling 1000 OpAmps cost allot more than 2000 gates no mater what form.In the serialized processing environment we commonly use redundancy to provide reliability. It wouldn't make sense to use another processor for arbitration because it would introduce a single point of failure.Discrete logic can have a latency well below 1nS. An equivalent serialized processor of any type would cost much more.The list of examples seems endless. These are the choices every designer makes to decide "why all the logic chips".In the beginning there was few choices but we still used the best option for each purpose. Now we have more choices because there are much larger overlapping specification boundaries.

author: westfw
author_rank: Super Contributor
timestamp: August 13, 2014, 06:05:21 am
content: QuoteAmen! This is easy to forget, now that you have $1 microcontrollers that contain all the peripherals and memory that you could ever want, for simple (and not so simple) functions.But in 1974, sort of the hay-day of 74xx TTL logic, something like a 7400 would cost $0.20 (on the hobbyist market), and the brand new 8080 microprocessor was several hundred dollars (just for the 8080), required a bunch of additional chips AND memory (which came in chips measured in bits (not even kbytes!) AND peripherals (which largely didn't exist; build them out of TTL!) AND multiple power supplies. And you needed a programmer (the person) as well, and those were hard to find (especially with EE skills too!)You can jump forward to the first flash or eeprom based microcontrollers (1993); before that you had to commit to having your firmware in ROM (only suitable for large volumes), External EPROM, or (some limited number of) chips with internal UV-eraseable EPROM and windows (expensive - you can still buy these) or One-time programmables (risky!)Cortex M3, the first ARM-based 32bit microcontroller was 2004.Dave has been tearing down a lot of older stuff, because it's more interesting. A modern gadget, with a microcontroller under a blob of plastic, and some connectors, is ... boring!(also, there are other sites that cater to the "Apple introduced a new iPad; let's take it apart!" crowd.)

author: bwat
author_rank: Frequent Contributor
timestamp: August 13, 2014, 06:41:42 am
content: Quote from: westfw on August 13, 2014, 06:05:21 amIt's not. We've had commercially available computers since, what, 1951 (the UNIVAC I was delivered in June 1951) which was 63 years ago. LSI came in the mid 1970s which was 40 years ago. That means it's not a newcomer relatively speaking. Relatively new would be the late 1990s.

author: 22swg
author_rank: Frequent Contributor
timestamp: August 13, 2014, 08:38:56 am
content: As an old timer who was weaned on TTL , CMOS and MSI, ( favorite was 8255 ) now hitting the dizzy heights of 16 bit mcu I still find use for an odd logic ic for example using a 74HTC04 to level shift I/O from 3.3v to 5v.

author: wigman27
author_rank: Regular Contributor
timestamp: August 13, 2014, 09:25:11 am
content: WOW!!I never expected such an awesome response from everyone! THANK YOU!I have a lot of thinking to do about this and certainly look into a few projects that I can do and include some logic, even completely logic chip based.I would love nothing more than to spend some time "Work Experience" learning professional circuit design and learning how things are implemented.I will have to keep my eye out for any opportunities that arise, unfortunately I don't think I could make a career move ass all of my studies are based around power but I would love to have the opportunity one day!Thanks again everyone!Lee

author: westfw
author_rank: Super Contributor
timestamp: August 13, 2014, 10:02:13 am
content: QuoteOh crap! That must mean I've gotten old!Perhaps we should have said "VLSI is relatively recent."Your Univac 1 had 5200 vacuum tubes ("valves.") THAT doesn't have anything to do with LSI."Computers" up through the mid 1980s tended to be based on relatively not very dense chips (2901 bitslices were very popular toward the end, there. Four bits of ALU per 40-pin DIP, and still much more powerful than most of the LSI-based microprocessor systems.)I'll stand by "flash program memory" being a significant event in the replacement of logic by microcontrollers, and that was the mid to late 1990s.

author: coppice
author_rank: Super Contributor
timestamp: August 13, 2014, 10:49:34 am
content: Quote from: westfw on August 13, 2014, 06:05:21 amThere are some errors there. In the late 80s/early 90s you could get EPROM microcontrollers which were practical for small scale production, but you needed to use the one time programmable (windowless) version to get any kind of reasonable price. Serious volume demanded masked parts, to get the cost down, and most EPROM microcontrollers had a masked counterpart.Flash microcontrollers started at the end of the 90s. Devices like the MSP430 started to establish a regime where development, small scale production, and large scale production could all be based on the same part. It was only in the mid 2000s that the big clunky emulators finally disappeared, and everyone was on board with flash parts, on board emulators and simple JTAG based debug tools.The first successful M3 microcontrollers were the STM32s, which I think came out in 2007. Well before that many people made ARM7 based MCUs, although most were notorious for being piles of junk thrown together from peripherals designs found in someone's waste bin, and never debugged. ARM7 was the biggest thing in controller cores, but not from sales of MCUs. It was from them being embedded in application specific devices, such as GSM chip sets, hard disk chip sets, and so on.

author: bwat
author_rank: Frequent Contributor
timestamp: August 13, 2014, 10:59:38 am
content: Quote from: westfw on August 13, 2014, 10:02:13 amThe UNIVAC I was chosen as the oldest commercial computer and at 63 years ago defines the start of the period, i.e. as old as old gets. It was the my main premise for LSI, at 40 years old, not being "relatively new".Quote from: westfw on August 13, 2014, 10:02:13 amFor some reason those were completely off my radar as a young nerd. It's only lately that I've realised that some of the CPUs which I regard as interesting were built with 2900 chips.

author: Wilksey
author_rank: Super Contributor
timestamp: August 13, 2014, 11:07:21 am
content: A handful of logic chips is cheaper than a microcontroller, and they work in parallel execution as people have already mentioned.An alternative which I use quite frequently is a CPLD or FPGA, but it's an expensive bit of kit (especially if you need an external PLD memory chip) for just an AND gate! My PLD/PGA's are usually doing a lot more so I just make the logic inside of the device as there is always some spare LE's and pins left.If I am not using a gate array or anything of the sort, and the micro won't cut it for timing / real time reasons etc then it just makes sense to put a 74 series chip on board, the only thing I find annoying sometimes is because they are usually quad devices (and are usually the cheapest) they can take up space on the board, but there are many different packages available these days that you will probably find something suitable whatever the requirement.If you have ever read a book on digital electronics you will know that the 74 series is the holy grail even if it to build a small circuit before putting it into a PLD/PGA or ASIC, unless I have read the wrong books

author: coppice
author_rank: Super Contributor
timestamp: August 13, 2014, 12:39:30 pm
content: Quote from: Wilksey on August 13, 2014, 11:07:21 amIf you don't need speed, a 25 cent MCU can replace a *lot* of simple logic chips. If you are paying, say, 6 cents a pop for 74HCxx devices, you'll break even at just 4 chips, and changes are wayyyyyyyy easier to implement cleanly in an MCU.

author: Wilksey
author_rank: Super Contributor
timestamp: August 13, 2014, 03:28:40 pm
content: But you don't have to program a logic chip....

author: WarSim
author_rank: Frequent Contributor
timestamp: August 13, 2014, 05:40:14 pm
content: Quote from: coppice on August 13, 2014, 12:39:30 pmYou are defending you opinion and ignoring the competing points.Yes at low time constraints a cheep uC could be less expensive.These are the points made that have been made that you seem to be missing.A cheep $0.25 uC can not supply <1nS latency of multiple gates.For a uC that can the power requirements will be much higher than That of a gate.Startup time is much lower with a gate than a uC.The support requirements and costs are higher. (In circuit programing/production programing/pre-programming all cost money) (all uC require more support passives than a gate)The question was why all the gates. People here gave valid reasons for opting for gates in certain circumstances. You are countering with over generalized noise. Do you have a point to add. Are we completely missing your argument for using a uC for situations that can not meet the required "real time" timing requirements mentioned?

author: amyk
author_rank: Super Contributor
timestamp: August 13, 2014, 08:41:52 pm
content: Quote from: WarSim on August 13, 2014, 05:38:20 amActually I mentioned that in my first post in this thread...Another reason for using individual gates over a CPLD or FPGA: there may be various places in the design that need a few gates, but they're spread out and trying to route all the signals into one CPLD/FPGA would be nearly impossible. I see this a lot in laptops - several dozen single or dual-gate devices are spread out over the motherboard and used for various "glue logic".

author: WarSim
author_rank: Frequent Contributor
timestamp: August 13, 2014, 10:20:27 pm
content: Quote from: amyk on August 13, 2014, 08:41:52 pmYes you did, apparently I missed it.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: August 14, 2014, 05:41:34 pm
content: The 7400 series is also ideal for teaching logic. Pins can be easily probed and the effects of non-ideal timing signals demonstrated.

author: tszaboo
author_rank: Super Contributor
timestamp: August 14, 2014, 09:00:23 pm
content: Quote from: coppice on August 13, 2014, 12:39:30 pmAnd, the 7400 or 4000 series logic IC (although, several have died over the years) you will be able to buy 30 years from now, while your DS80C310-QCG/T&R-ND might not be able to buy tomorrow.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 14, 2014, 11:03:42 pm
content: To be fair, most programmable logic have life cycles much longer than you'd expect. Altera Cyclone I and II are still around, I think the first is finally NRND or discontinued? Altera at least seems to give a 10+ year life cycle.And some things never go away, like PALs/GALs, which are still on Digikey no less.Tim

author: WarSim
author_rank: Frequent Contributor
timestamp: August 15, 2014, 03:54:36 pm
content: Funny how a single decade is considered a long time now. A decade is even called forever by the dramatic.

author: BloodyCactus
author_rank: Frequent Contributor
timestamp: August 15, 2014, 04:01:09 pm
content: for me, I have some logic chips in my design in the watchdog circuit because I need to rely on something other than the MCU if the MCU does something wonky, so all the watchdog circuitry needs to be stand alone.

author: david77
author_rank: Frequent Contributor
timestamp: August 15, 2014, 04:37:37 pm
content: Quote from: wigman27 on August 12, 2014, 12:30:35 pmAs has been explained already there was a time when there were no cheap and easy to program micros to make things, so one had to use discrete logic. For many simple logic functions even today it's easier and cheaper to use a few logic gates.In 2007 I made this board that only latches & debounces three pushbuttons and an up/down counter with two more buttons that can count from 1 to 8. I used it in my home brew preamp for my stereo system. The up/down counter lets me select inputs 1 to 8 and the other buttons control things like tape monitor and mute. The board controls a bunch of relays on another board via a four wire BCD connection.Doing it with a micro would have been much much easier but I really learned something from it and am now reasonably confident in using discrete logic. Btw. this thing is still in use nearly every day 7 years later.

author: coppice
author_rank: Super Contributor
timestamp: August 16, 2014, 03:56:49 am
content: Quote from: NANDBlog on August 14, 2014, 09:00:23 pmPerhaps. I wouldn't guarantee it, though. "Several" is a massive understatement. Most of the logic families that were common 30 years ago are no longer available - ECL, RTL, DTL, etc. Only a small part of the 74xx range and 4xxx range can still be obtained, and you can't generally get the originals. Being original might be important if you relied on a quality like output drive. Only the simpler 74xx and 4xxx parts can still be obtained. The more complex ones are no longer useful, and so have disappeared. People still need simple stuff as glue, so there is still a huge market for those.I agree that logic tends to hang around longer that most MCUs, but you can still gets clones of some 30 year old MCUS, like the 8048, often still implemented as NMOS. I think someone is still making TMS1000 clones, which was the very first MCU in the 1970s.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 16, 2014, 05:07:39 am
content: ECL is still alive and well:http://www.digikey.com/product-detail/en/MC10H101PG/MC10H101PGOS-ND/1478129for instance, original 10k ECL.Not sure what all variants used to be around that have since fallen out of favor...I don't think RTL/DTL is any loss, as they were largely compatible with TTL(??), and simply technically inferior (relics from a time when every transistor was precious). If you need to find replacements that meet timing and pinout, have fun with that, but the functions and signals haven't gone away.Likewise with almost all 7400, which were inferior to LS for the most part. Some things, like 7406, don't make sense, or can't be made, in other families (30V outputs!), so they stuck around.Most of the esoteric 7400 have died off, and weren't remade in LS. All the important (and compatible) 7400/LS were also pushed into HC (and the related HCT, AC, etc.), as well as many of the cooler 4000 series functions. And then LVC and "Tiny" families and so on.I wouldn't say it's so much a matter of things dying off, as things being streamlined. Requirements are always changing, so the demands of glue logic vary a bit, but the basics obviously have weathered well. The same is true in general at all levels of computing: from glue logic to 8-bit micros (4 bit, even!) and on up the ladder, the lowest level requirements willnevergo away.Tim

author: coppice
author_rank: Super Contributor
timestamp: August 16, 2014, 06:32:08 am
content: Quote from: T3sl4co1l on August 16, 2014, 05:07:39 amInteresting. Motorola killed them. On must have found a application which justified them being brought back.Quote from: T3sl4co1l on August 16, 2014, 05:07:39 amDTL is only compatible as a fudge. Its thresholds are different from TTL, and mixing them doesnt' always work. DTL definitely isn't a drop in replacement. RTL was not compatible at all.Quote from: T3sl4co1l on August 16, 2014, 05:07:39 amYou can't necessarily use an LS part to replace a non LS part. The drive is lower. This isn't so relevant to the 30 year period being considered, as LS had already supplanted non-LS by then.Quote from: T3sl4co1l on August 16, 2014, 05:07:39 amMost of the esoteric stuff only existed in LS form, and has gone with the wind. An HCT or HC part may of may not be a suitable substitute for an LS part. The drive levels differ. The thresholds may differ. The switching characteristics certainly differ. Only the essential logic function persists through these families.Quote from: T3sl4co1l on August 16, 2014, 05:07:39 amThe bottom line is its pot luck whether your favourite part will be around in a suitable form in 30 years. You can tell that some stuff will clearly not be available in 30 years, because it will be utterly irrelevant. Saying some form of 74xx will still be available in 30 years is like someone in the 1960s saying the 6L6 and EL34 will be around in 30 years. They actually were, but only because of one application - guitar amps. Nothing else (such as audioxfiles) would have generated the volume needed to keep even small makers interested. It was just pot luck.

author: SeanB
author_rank: Super Contributor
timestamp: August 16, 2014, 06:43:35 am
content: TTL bus buffers are very likely to still be here in 30 years, just because they are so veratile and very common in equipment, as most microprocessor bus outputs are not capable of high current drive or long line driving ( over 20cm or 5 loads), so you find a LS244/245 or the 5XX series ones in common use. HC138 is also still common as a decoder as well, it is often simpler than using part of a logic block to split out the address lines or to save pins.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: August 16, 2014, 07:10:05 am
content: Quote from: coppice on August 16, 2014, 06:32:08 amRe: Audiophools and tubes: I wouldn't be so sure. Sure, the audiophool marker may be 10-100 smaller than the guitar amp market, but those are the kind of people that would easily pay 10-100 times more than the current market price. So it might very well have been economically viable even if the guitar amp market for those tubes didn't exist.That aside, I think key factors here are how easy something is to manufacture, and what the demand for it is. A vacuum tube is an oddball device to manufacture today. it would obviously require its own manufacturing procedure etc. A CMOS logic chip on the other hand, is "just another device", as long as other devices with similarly specced silicon are being manufactured. As for the demand, I don't see the demand for some glue logic here and there going away completely any time soon. For this to happen, something would have to replace it. In the case of guitar amps, this would be DSP amp modeling, which is prevalent, even if some people swear by the original sound. In the case of glue logic, one way this could happen is that in 30 years, even the cheapest piss and microcontrollers are expected to have a small programmable logic area, much like we expect even the cheapest micros today to have things like an internal clock driver, at least some internal memory and some UART or SPI type communication built-in.

author: tszaboo
author_rank: Super Contributor
timestamp: August 16, 2014, 08:37:56 am
content: Quote from: coppice on August 16, 2014, 03:56:49 amWell, maybe the TMS1000 will be still copied, but the things made after, I wouldn count on it. The types of MCUs jumped from a dozen to several thousand, so there is just not time and effort to copy all. If you see, every time Dave opens something, he immediately finds the logic chips and knows what they are, while with MCUs, lot of times even the manufacturer is not around anymore.The RTL appeared in 1961-2 and made it in space in 1969 (or around). By that time, even if this wasnt said, it was NRND, as there were several better families. So I would say that 30 years ago it was common, I would say 30 years ago designing something with RTL or DTL would have been a large mistake.I'm not against MCUs. They are good when it comes to reducing cost, size, complexity often times.

author: 22swg
author_rank: Frequent Contributor
timestamp: August 16, 2014, 07:43:12 pm
content: The 74 TTL era was a great time to learn and develop ideas , with a strip board and iron (fe)a hand full of TTL / 4000 anything was possible . Having seen David77'sboard picture thought I would post my 1980's interface, I was learning to play an Elka E19 organ but fancied some better sounds from a TG100 midi box so I designed and built this board, it would still work but i removed the MAX232 for the next version an mcu ! no longer have the E19 ... got a Tyros with my redundancy cash !

author: westfw
author_rank: Super Contributor
timestamp: August 16, 2014, 10:35:50 pm
content: One of the nice things about the 74xx and 40xx series was that they were sufficiently popular and long-lived that many chips with the same functionality and pinout have been released in newer technologies. You may not be able to find a viable source of 7400 chips, but you can certainly find other 74xxx00 quad nand gates in the same 14pin package(s.) And the larger functions that have survived have been "proven" to have useful bells and whistles (presets, clears, combinations of enable inputs, etc.)It's pretty much the nature of "logic" that it doesn't need to "stay around" in exactly the same form. Most of the circuits you build with 74ls logic will do just fine converted to 74lvhc or whatever. Yeah, you occasionally see circuitry that relies on electrical behavior other than boolean algebra, but it is relatively uncommon. (Particularly, compared to a microcontroller design that relies on a certain instruction set (all of them?) or peripherals...)

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2014, 09:58:13 am
content: Quote from: NANDBlog on August 12, 2014, 08:58:07 pmI agree, one of the nice thing about the 4000 series is the wide power supply voltage range. Most MCUs will work from 5.5V (6V at a push but not recommended) so you need an additional IC for that, plus logic level shifting if it needs to interface with higher voltage circuitry.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 18, 2014, 12:48:19 am
content: Not to mention the CD4007 (transistor array -- who needs gates in a logic family?), CD4049U (CMOS pairs -- inverters, unbuffered, no input protection diode to VDD -- vs. the '69 which is the normal CMOS design), CD4046 (PLL, osc with reasonable linearity, little or no dead zone in the one phase detector -- apparently unmatched by the botched variants 74HC4046 and 74HC7046) and more. Needless to say, analog switches are cool, too.

author: 22swg
author_rank: Frequent Contributor
timestamp: August 18, 2014, 08:32:47 am
content: Really useful are the analogue switches. 4067, 4051, and 4016 ... beginning to miss them already

author: SeanB
author_rank: Super Contributor
timestamp: August 18, 2014, 06:20:45 pm
content: 4049/50 is great as a level translator to run inputs into 5V logic from 15v or so inputs, or from 12V from external switches. Also great on circuits where you depower parts and do not have to worry about them being powered via logic inputs, or dragging the logic levels down.OTOH, who needs a MCU when you can use a board full of CMOS to do the logic work, like this Sony controller in a Umatic deck.