PLC (code) today is a High Level script rule language running on a embedded controller. One can design and write the code for a PLC as an embedded programmer but it's rare that PLC coders could do the same.

The magic of the controller is the ability to combine several types of different functions into a single device (sometimes to excess). It makes a huge amount of engineering and economic sense to integrate many small logic functions (photo sensor, indicators, jumper inputs, status/error lights, limits , etc..) into a more general set of easily modifiable system functionality that easily justifies the cost of a cheap 8-bit controller.

I'm from the day when discrete logic design was still in vogue. Lot's of TTL devices enabling pins without using a microcontroller. The controller (8080) did raster operations on graphics commands to format the frame buffer data for NTSC video display.
https://forum.allaboutcircuits.com/...ro-programming-experience.180316/post-1646882

 

OK, Max, consider that the CNC machine without all of that analog I/O to make the motors run the right way at the right time is only a small box with a keypad, knobs, and a display. Fun to fiddle with but not very useful, except maybe to tell a machine operator what to do next.

I am not sure I would want to put together a CNC controller with discrete components, !
Current DIY CNC systems do not use any analogue, all digital.
The professional DIY 8 axis CNC Galil Motion cards I have used Implement features that if anyone where to try and replicate them using discrete logic , they would deserve the Nobel Prize!
One e.g. Gear 7 axis off of one encoder!

 

Inside every motor driver is analog circuitry. The controls connection interface is digital, but the actual drive is not. You just never see it because it is in the box that works so very well. Inside the encoders you will find analog, working so well that you never need to see it. The interconnections of course are digital, and that ties the blocks together.

 

Inside every motor driver is analog circuitry. The controls connection interface is digital, but the actual drive is not.

In the case of the A-M-C DC/BLDC motor drives I use, they do use analogue input, as they are transconductance amplifiers, the rest is all digital, I have repaired a few.
Also all the ECM motors now used in HVAC and washing machines, (e.g. Fischer-Paykel), are all digital controllers.
No analogue.

 

Inside every motor driver is analog circuitry. The controls connection interface is digital, but the actual drive is not. You just never see it because it is in the box that works so very well. Inside the encoders you will find analog, working so well that you never need to see it. The interconnections of course are digital, and that ties the blocks together.

That's simply not true. Your comments shows a shallow understanding of modern digital circuits ability to generate motor drive signals in realtime using fast controllers.

https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1531704
https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1550621

These two-phase motor drive signals are completely digitally generated. There is no analog analog source signal that feeds any analog stage, only an output filter to remove the PWM carrier from the digital modulation and current feedback from the H-bridge to the controller ADC for software limited circuit protection.

 

That's simply not true. Your comments shows a shallow understanding of modern digital circuits ability to generate motor drive signals in realtime using fast controllers.

https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1531704
https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1550621

These two-phase motor drive signals are completely digitally generated. There is no analog analog source signal that feeds any analog stage, only an output filter to remove the PWM carrier from the digital modulation and current feedback from the H-bridge to the controller ADC for software limited circuit protection.

View attachment 271147View attachment 271148

OK, so only the actual current in the windings is an analog variable. I concede on that one.

 

Inside the encoders you will find analog, working so well that you never need to see it.

Also, the only thing considered analogue on the popular incremental/quadrature encoder is at detection from the photo diode, it is immediately squared up, and from there on is digital.

 

OK, so only the actual current in the windings is an analog variable. I concede on that one.

A good understanding of analog is still necessary to understand how things like Sine and FOC work because, as you say the current in the coils is a analog signal, that behaves with classic time-varying currents properties that must be handled in the digital domain using transformations that can track load changes dynamically within a cycle while improving efficiency over traditional motor drives.
https://training.ti.com/demystifying-bldc-motor-commutation-trap-sine-foc