Author Topic: Are Logic Circuits Still Used or Micros  (Read 31047 times)

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Offline bostonmanTopic starter

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Are Logic Circuits Still Used or Micros
« on: March 10, 2024, 03:20:20 pm »
I'm uncertain if this question belongs in the Microprocessor section, but it's somewhat simple.

At an old job we had timing circuits that used regular logic gates and flip-flops. Eventually the newer designs incorporated FPGAs and I no longer saw logic circuits. My last few jobs seem to always use micros (i.e. software) to handle the logic now.

Are logic gates being phased out and replaced with micros to save room and money?
 

Offline themadhippy

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Re: Are Logic Circuits Still Used or Micros
« Reply #1 on: March 10, 2024, 03:45:02 pm »
no,the logic gates just got smaller and loads of em fit in the thing we call a micro.
 

Offline bostonmanTopic starter

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Re: Are Logic Circuits Still Used or Micros
« Reply #2 on: March 10, 2024, 03:53:41 pm »
Does this mean the days of seeing an array of logic gates and flip flops are ending?

If more logic is being placed into what we call a micro, that means the code will now be dealing with the logic making it harder to repair electronics, correct?
 

Offline pcprogrammer

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Re: Are Logic Circuits Still Used or Micros
« Reply #3 on: March 10, 2024, 03:58:00 pm »
no,the logic gates just got smaller and loads of em fit in the thing we call a micro.

That is just mean  :-DD

It is also what sits at the heart of FPGA's for that matter, but there will always be room for standard logic IC's. Sometimes you just need to invert a signal and with the availability of single gates it is probably cheaper than using a microcontroller. Or you need to shift between voltage levels. Logic IC's come to the rescue.

Does this mean the days of seeing an array of logic gates and flip flops are ending?

If more logic is being placed into what we call a micro, that means the code will now be dealing with the logic making it harder to repair electronics, correct?

Not at all. FPGA's have there niche, as well as logic IC's.

Sure a lot of things can be done with microcontrollers, but there are speed limits.

Edit:

Electronics getting smaller and smaller is what makes repairs more difficult. This is just a continuing line, like TV's used to be based on valves, then transistors, then dedicated IC's, also making it harder to fix a TV, unless a part could be sourced.

With microcontrollers it is the same, but you also need the firmware, which might be more difficult.
« Last Edit: March 10, 2024, 04:01:53 pm by pcprogrammer »
 

Online Benta

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Re: Are Logic Circuits Still Used or Micros
« Reply #4 on: March 10, 2024, 04:10:20 pm »
I use a lot of standard logic ICs, both for logic, but especially for timing. Mostly 74AC or 74HC, but sometimes also 4xxx series.
CPLD/FPGAs could do it as well, but the problem is that their power consumption is horrendous. The lowest power CPLDs I've managed to find burn 100+ mA, where my standard logic will need less than 5 mA.

 
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Offline bostonmanTopic starter

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Re: Are Logic Circuits Still Used or Micros
« Reply #5 on: March 10, 2024, 04:18:13 pm »
I should clarify "logic" being more at the level of AND, OR, and basic flip flops.

Absolutely correct that sometimes a simple circuit will require a few gates, so a micro (or FPGA) would be a waste of money.

As mentioned, I've seen a shift where it's been years since any circuits at a company I've worked for use logic gates. It makes sense because the things some of the micros use in existing circuits I'm working with would take an array of gates to perform, so I get it, but scary because A: I don't know how to program these micros and B: it's another step towards being unable to repair our own electronics.
 

Offline mikeselectricstuff

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Re: Are Logic Circuits Still Used or Micros
« Reply #6 on: March 10, 2024, 04:47:11 pm »
Does this mean the days of seeing an array of logic gates and flip flops are ending?

If more logic is being placed into what we call a micro, that means the code will now be dealing with the logic making it harder to repair electronics, correct?
But fewer parts also make things more reliable so less likely to need repair.
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Online IanB

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Re: Are Logic Circuits Still Used or Micros
« Reply #7 on: March 10, 2024, 04:57:26 pm »
In my first job, we had some logic implemented with pneumatic logic gates. It made sense because it was in an environment unfriendly to electronics, there was no need for an electrical power supply, the compressed air to run it was already available in the industrial setting, and the state of the logic was easily observed.

Those conditions that applied then would likely still apply today.
 

Offline T3sl4co1l

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Re: Are Logic Circuits Still Used or Micros
« Reply #8 on: March 10, 2024, 05:03:35 pm »
Glue logic isn't going anywhere.  There's just less of it used in any given place, compared to the bad old days when you needed, say, whole cards of the damned stuff to accomplish much of anything.

Give or take, if you need more than two or three chips to do the job -- just toss it in a micro, or FPGA.  Occasionally you find an ASIC which does the function as well -- more and more highly-specialized chips appear on the market, day by day.

It's rare that it's economical or otherwise worthwhile to build even a fairly modest function out of hardware logic, let alone because, if you need to make changes coming up to or following release, you're SOL with hardware, but firmware can be updated.

Mind, it may cost more to write that firmware.  If you're doing a few-off sort of thing, and the application is well defined, the break-even point might be more like dozens of chips worth of logic.

Which one, MCU or FPGA, depends on how fast and accurately (mainly in terms of timing) you need the result.  FPGAs are excellent for electronic interfaces and high bandwidth systems; it's nigh impossible to interface even a high-performance MCU to something like a vintage PC or console bus, but trivial for an FPGA.  (Some MCUs do in fact include bus interface hardware, or complex timers, SPI or other peripherals which can be used in these ways.  Some even include whole state machines, like RP2040's PIO.  Or specialized devices with very high granularity per pin or group, like XCore.)  For everything else, the grade of MCU dictates how much processing and bandwidth can be done, within a modest (often poorly defined, due to inconsistent timings: execution path variation, cache stalling, interrupt overhead, etc.) time frame, say µs to ms, and up.  Top-of-the-line CPUs (ARM64, amd64, RISC-V, etc., with zillions of extensions each, and often paired with even more impressive vector-data and array-CPU style GPUs) offer many GFLOPS of performance, even just as a starting point, let alone with all the cores brought to bear (TFLOPS are available!).


I use a lot of standard logic ICs, both for logic, but especially for timing. Mostly 74AC or 74HC, but sometimes also 4xxx series.
CPLD/FPGAs could do it as well, but the problem is that their power consumption is horrendous. The lowest power CPLDs I've managed to find burn 100+ mA, where my standard logic will need less than 5 mA.

AFAIK, CPLDs are obsolete -- give or take exact design and functionality, as there is a lot of overlap with FPGAs, but classics like MAX5k/7k were so ridiculously thirsty due to use of EEPROM programming.  Basically as I understand it, it's NMOS logic, where the logic functions are programmed in via floating gates.  There's no complementary EEPROM (or, it's not worth setting up complements and the programming logic to set them) so it's either off or sinking bias current.  In an E(E)PROM (chip, as such), you only get that current consumption during a read cycle, here it's 100% always-on; ridiculously inefficient.

Modern FPGAs do... other things; what, I'm not up to speed on, but an example is a Flash block off to the side, that's copied into SRAM automatically during startup (which does cost a few ms at power-on, which can be prohibitive in those weird applications when you really do need instant-on function).  AFAIK, external configuration Flash is still very common as well (the chip is read in via SPI or whatever, filling SRAM tables -- LUTs, logic arrays, etc.).

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Offline pcprogrammer

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Re: Are Logic Circuits Still Used or Micros
« Reply #9 on: March 10, 2024, 05:22:28 pm »
Modern FPGAs do... other things; what, I'm not up to speed on, but an example is a Flash block off to the side, that's copied into SRAM automatically during startup (which does cost a few ms at power-on, which can be prohibitive in those weird applications when you really do need instant-on function).  AFAIK, external configuration Flash is still very common as well (the chip is read in via SPI or whatever, filling SRAM tables -- LUTs, logic arrays, etc.).

Yep. Some do have internal flash memory for the configuration but external is most common. With large ones and predefined memory parts the configuration can be very large and take quite a while to load. Also depends on the default speed of the used interface. For most it is possible to do it with a CPU host based on serial or parallel to speed it up a bit, but still.

They are very versatile though.

Offline tooki

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Re: Are Logic Circuits Still Used or Micros
« Reply #10 on: March 10, 2024, 05:53:48 pm »
Are logic gates being phased out and replaced with micros to save room and money?
Let’s take that and replace it with a modified question: Are discrete logic products being phased out?

No. The fact that TI and co continue to release new logic products (like tiny SMD packages containing a single logic gate) and even entirely new logic families (like TI did a few years ago) are a strong indicator that they’re not going away.

Now let’s address the question you probably meant: Are entire circuits made of discrete logic parts going away?

Yes, to a large degree. It’s easier and cheaper to use a MCU or FPGA (depending on the application) most of the time.


So how does one reconcile the seemingly-contradictory answers to these questions? T3sl4co1l already did: glue logic. We aren’t designing entire circuits around discrete logic much, but we use discrete logic to help out here and there. You might need a level shifter or line driver. Or you might need to perform a hardware-level logical operation on some signals (so that they cannot fail due to a software bug, or because they need to be much faster than an MCU, or because the output goes to an MCU pin that isn’t under software control, like a reset line or bootstrapping pin.)
 
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Offline HwAoRrDk

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Re: Are Logic Circuits Still Used or Micros
« Reply #11 on: March 10, 2024, 05:57:42 pm »
I can't speak for industry trends in general, but I was recently working on a design where I was needing some fairly simple gating/latching logic for power switching. I came up with a design using three 74-series logic ICs which would've done the job. But then I realised I can buy a cheap MCU that does it all for the cost of just one of the logic ICs. Sure I now have an extra assembly step of programming the MCU, but that's a trade-off I was willing to make.
 
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Online tggzzz

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Re: Are Logic Circuits Still Used or Micros
« Reply #12 on: March 10, 2024, 06:00:34 pm »
Does this mean the days of seeing an array of logic gates and flip flops are ending?

No. Just look at distributor cataloges.

Interestingly, logic gates are being split out so there is just one in each package; e.g. see the 74LVC1G* devices. 1G implies 1 gate so a 74LVC1G04 contains a single inverter, or a '00 contains a single 2-input NAND gate.

Quote
If more logic is being placed into what we call a micro, that means the code will now be dealing with the logic making it harder to repair electronics, correct?

Yes.
« Last Edit: March 10, 2024, 06:04:58 pm by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
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Online tggzzz

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Re: Are Logic Circuits Still Used or Micros
« Reply #13 on: March 10, 2024, 06:04:05 pm »
In my first job, we had some logic implemented with pneumatic logic gates. It made sense because it was in an environment unfriendly to electronics, there was no need for an electrical power supply, the compressed air to run it was already available in the industrial setting, and the state of the logic was easily observed.

Those conditions that applied then would likely still apply today.

I was once asked whether to replace such (2000psi?) logic with a micro.

Given that the gas was propane on an unmanned offshore oil platform, it seemed to be a difficult proposition :)
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline mikeselectricstuff

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Re: Are Logic Circuits Still Used or Micros
« Reply #14 on: March 10, 2024, 06:08:33 pm »
Now let’s address the question you probably meant: Are entire circuits made of discrete logic parts going away?
Not just gone, but long gone, like 20+ years ago. Almost anything that needs more than a few 74 series packages will be simpler, cheaper & more flexible to do with an MCU
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Online tggzzz

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Re: Are Logic Circuits Still Used or Micros
« Reply #15 on: March 10, 2024, 06:11:26 pm »
Now let’s address the question you probably meant:
...

Yes, answering a question is easy.

Asking the right question is more difficult - and more important.

Some of the people I've really respected have the knack of asking a simple question, the answer to which illuminates whole areas of the topic.

For software systems one such question is "what do you mean by identity?", or the very similar "what is the meaning of an address?".
For digital hardware systems, "what are the clock domain boundaries?".
There are lies, damned lies, statistics - and ADC/DAC specs.
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Online PCB.Wiz

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Re: Are Logic Circuits Still Used or Micros
« Reply #16 on: March 10, 2024, 07:12:05 pm »
Are logic gates being phased out and replaced with micros to save room and money?
Broadly, yes.
Of course, it does need to 'save room and money' which means Logic Gates will never go away entirely.
If you pop over to lcsc and search MCU and Logic, you find higher stocks of logic, focused mainly on single gate parts, with 8 bit shift registers popular too, and analog switches.

I should clarify "logic" being more at the level of AND, OR, and basic flip flops.

Absolutely correct that sometimes a simple circuit will require a few gates, so a micro (or FPGA) would be a waste of money.

As mentioned, I've seen a shift where it's been years since any circuits at a company I've worked for use logic gates.
It makes sense because the things some of the micros use in existing circuits I'm working with would take an array of gates to perform, so I get it,
but scary because
A: I don't know how to program these micros and
B: it's another step towards being unable to repair our own electronics.

A: is easily solved. Learn how to program them :)
B: has been here a long time already, the very small parts are hard to identify and source.
 

Offline Siwastaja

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Re: Are Logic Circuits Still Used or Micros
« Reply #17 on: March 10, 2024, 07:27:58 pm »
Large boards full of logic ICs, implementing complex functionality, are gone. Need for some relatively simple glue logic (orring many signals, muxing/demuxing, schmitt triggering, level conversion, bus isolation, ...) hasn't gone anywhere. This is often just 1-2 parts next to a microcontroller.
 
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Online artag

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Re: Are Logic Circuits Still Used or Micros
« Reply #18 on: March 11, 2024, 12:02:54 am »

If more logic is being placed into what we call a micro, that means the code will now be dealing with the logic making it harder to repair electronics, correct?

Most manufacturers only care about manufacturing costs, not repair costs.
For some high-value items, repair costs may be important. But repair costs with micros can also be lower - no need to troubleshoot a board full of logic, just replace a subassembly (might be a micro).
Repair costs for someone without access to company information and spares supplies are very unlikely to feature in any manufacturer's decisions.
 

Offline bostonmanTopic starter

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Re: Are Logic Circuits Still Used or Micros
« Reply #19 on: March 11, 2024, 04:28:35 am »
Thanks for the feedback and this confirms my observation.

Quote
A: is easily solved. Learn how to program them

You're absolutely correct. ST MCUs seem to be popular; unless I'm wrong. Maybe it's time I begin diving into these a bit to learn some of the basic structure.

Replacing an entire board dedicated to logic chips with an MCU makes sense, do get it and understand the cost/space savings. It just upsets me when I want to repair something and see a MCU or EEPROM because I know it can't be replaced if it's suspected bad.

 

Online SiliconWizard

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Re: Are Logic Circuits Still Used or Micros
« Reply #20 on: March 11, 2024, 04:38:30 am »
It depends.
 

Offline T3sl4co1l

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Re: Are Logic Circuits Still Used or Micros
« Reply #21 on: March 11, 2024, 07:42:26 am »
MCUs are identifiable; there is a great diversity of them available, but many aren't beyond reach.  The main problem is lack of firmware, and most commercial products will set the lock bits that (nominally) prevent readout.  Even with readout, you only have a binary blob, no debug symbols; reverse engineering is a chore -- but still quite tractable with help of decompilation tools like Ghidra.

There are hackers working on many prominent commercial products; very hit-or-miss of course, mainly when poor behavior, locked or malfunctioning features inspire a user to engage at such length.  This includes unlocking readout, which is often an internal firmware check susceptible to power supply glitching, or with still more investigation, perhaps a zero-day can be found that allows reading out arbitrary memory and thus the entire firmware.  USB and network devices are staples of this, often USB by abusing the descriptor offset/length (it's just copying out some memory somewhere), network by abusing packet sizes, parsing, any manner of web server or other protocol, etc..

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Offline Alex Eisenhut

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Re: Are Logic Circuits Still Used or Micros
« Reply #22 on: March 11, 2024, 09:53:40 am »
In my first job, we had some logic implemented with pneumatic logic gates. It made sense because it was in an environment unfriendly to electronics, there was no need for an electrical power supply, the compressed air to run it was already available in the industrial setting, and the state of the logic was easily observed.

Those conditions that applied then would likely still apply today.

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Offline Berni

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Re: Are Logic Circuits Still Used or Micros
« Reply #23 on: March 11, 2024, 10:22:50 am »
Replacing an entire board dedicated to logic chips with an MCU makes sense, do get it and understand the cost/space savings. It just upsets me when I want to repair something and see a MCU or EEPROM because I know it can't be replaced if it's suspected bad.

We already had this as far back as the 1980s. There is plenty of test equipment from that time that is full of EPROMs, ROMs, microprocessors etc.. And i had cases of them failing (tho the awesome people of this forum helped me find a binary image of the chip contents). The difference back then is that microprocessors were awfully expensive (since they were the latest and greatest in chip manufacturing technology) and so only expensive professional equipment could afford to use then inside their BOM.

So cheap consumer products had 2 options:
1) Dumb down the features of the product so much that it is viable to implement in a handful of standard chips.
2) Create a ASIC for the most complicated parts and make sure you are making a product with a large enough market to justify the price of developing the ASIC.

So the result is that the old products are either full of mostly analog circuitry (radios, TVs, toys..etc) or the product is based around a special ASIC that does everything (Calculators, digital watches..etc) and is often encapsulated under a black epoxy glob (since that's cheaper than a chip package)

In these modern times products have gotten so complex that it is infeasible to implement them with standard chips, while at the same time MCUs have gotten so cheap that they are viable for replacing even fairly simple analog circuitry.

Just look around you at various products and imagine implementing them without a MCU somewhere deep in there. Things like TVs, monitors, webcams, USB microphones, bluetooth speakers, wireless game controllers, modems, WiFi routers, induction cookers with capacitive buttons...etc
 

Offline bostonmanTopic starter

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Re: Are Logic Circuits Still Used or Micros
« Reply #24 on: March 11, 2024, 01:17:37 pm »
Quote
Even with readout, you only have a binary blob, no debug symbols; reverse engineering is a chore

Reverse engineering probably isn't a necessity as obtaining the code to burn a new chip in order to replace a suspect failed chip. Maybe I'm wrong, but people are pushing for the "right to repair", however, electronics with programmed chips (whether an EEPROM, MCU, etc...) can't be repaired without obtaining a replacement from the company. In my limited experience, I've never had success purchasing a programmed component from a company. Most times the response I get is to send the unit back for evaluation/repair at a ridiculous cost, no response at all, or some generic response about the apologizing for issues I'm experiencing.



 


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