Of what use can an analog logic gate be to a circuit that contains a micro-controller

[nullexception]

I am wondering if a logic gate would be of use to a circuit that contains a micro-controller.Are there cases when an analog logic gate is proffered over a micro-controller and what are some of the gadgets that use analog logic gates in the age of micro-processors and controllers.

 

[Tunelabguy]

On example is a logic-controlled analog switch used for synchronous detection of a period analog signal.

 

[nullexception]

On example is a logic-controlled analog switch used for synchronous detection of a period analog signal.

But this is rare,dont you agree?.

There is almost no need to have logic gates if you have a micro-controller i hypothesize,is this correct?.

 

[Tunelabguy]

If you think "logic gates" are an alternative to a microcontroller, then you must have some specific idea of what a "logic gate" is. Perhaps you are thinking of the old-fashioned "analog computer", which was a way of modeling real-time physical processes using op-amps. That indeed is supplanted by digital simulations on digital computers. If you have some other meaning of "logic gate", you will have to explain yourself. But as for "rare" applications, many applications are rare, but still they may be appropriate for those applications that need them. Not all applications need synchronous detection of periodic signals, but for those that do, an analog switch is often just the right solution.

 

[FvM]

I guess the OP phrased his question unclearly and is asking about regular digital logic gates.

 

[Dan Mills]

Thing is microcontrollers are sequential machines, which is fine for a lot of use cases.

However there are plenty of occasions where you need things to happen without the use of a clock, and somw where timings are measured in terms of a few tens of ns, difficult to do that with a micro, but very easy with some glue logic or a small gate array.

Something like a delta sigma modulator is easy in an FPGA, but you try to get it fast enough in a micro....

Or take for example a 50MHz clock, and a requirement to divide it down to something slower, say 12.5MHz such as one may use to clock an AD converter, this is trivial with a couple of flipflops but practically impossible using a program running on a micro (Some have on chip counter timers that may make it possible).

Another case where discreet logic is sometimes preferred is in safety critical systems where having a very small state space makes verification much easier, with only a few bits of state I can reason about the system fairly easily, less so when I have a KB of ram...

Sometimes there are things you could do in software, but that are so much easier and more reliable in hardware that you find yourself placing a picogate or so just because it makes the need for tricky interrupt back magic to meet some timing constraint go away (And besides hardware interlocks on syncronous gate drivers for example are a good thing).

Micros are useful tools, but all tools have their place.

Regards, Dan.

 

[Tunelabguy]

I guess the OP phrased his question unclearly and is asking about regular digital logic gates.

Oh, if that is the case, then my answer is that logic gates (or FPGAs, which are functionally the same thing) are still the best solution in many cases. In addition to the excellent reasons given by Dan Mills, I would just add that the cost of implementing a logic function in software is not zero. Software takes up program space. But more importantly, it takes up execution time. Software that implements a logic function must be actively polled in order to perform the the same as a logic gate. This polling detracts from the responsiveness of the main application. In some applications with a processor that is way more powerful than needed, this extra processing time may not matter. But in good designs with little margin, extra polling cannot be added willy-nilly. Finally, there are battery-powered applications where the processor is asleep most of the time. For such applications, a CMOS logic gate can continue to function with almost no power, while the equivalent running processor doing the same thing will consume orders of magnitude more power and run down the battery.

 

[chuckey]

One microcontroller I came across scanned 144 I/O lines with external multiplexers and drove a network (Bitbus), so I guess that a few logic chips were involved in that.
Frank