Earlier quoted context omitted.
The problems are power consumption, speed, cost, size, development time, and the difficulty of updates and bug fixes. A modern embedded processor handily solves all of those. Boards full of TTL are a fascinating engineering exercise, but there aren't many applications where they're a better solution. It's also tempting to cheat and solve some of the sub-problems with monostables and analog timers. As soon as you do t…
> power consumption That's the only one I don't quite understand. All your other points are definitely great objections. Are you saying that a clocked system consistently uses less power than a stateful but quiescently 'static' circuit? I can imagine there's a reason, but it goes counter to my experience that the faster you clock a microprocessor the more power it consumes; therefore at zero clock rate a purely data-…
1. Discrete logic chips tend to be built in substantially larger process nodes (microns vs nanometers) that are less efficient. This means higher leakage current and more static power.
2. Discrete logic has to drive traces on a PCB, which have substantially higher capacitance (C) and therefore use more power getting across a board.
3. Discrete logic operates at higher voltages. Contrast 5V TTL vs. 1V core voltage inside a processor. Power is proportional to the voltage squared.
4. A microprocessor running even at low speed can replace a massive number of discrete logic chips, so for simple solutions F is low. If you're doing something very simple and interrupt-driven, F can be in the tens-hundreds of kHz.
Consequently, there's a whole lot more of both static and dynamic power with discrete logic than with a uC.