Im really confused by what field programmable gate arrays are and what they do. What is digital logic also and how do FPGAs relate to CPUs? Please eli5
In: Engineering
Wait, you don’t understand digital logic? Then you don’t stand a chance of understanding FPGAs. So let’s start there:
Digital logic circuits do (almost) everything based on “logic states”, and there are only 2 possible states in a binary digital logic circuit. We call these “on and off”, or “true and false”, or “1 and 0”. For example, imagine a light bulb wired to a battery through two switches in series, A and B. The light is turned on only if both A *and* B are turned on. So that’s a binary digital logic AND gate.
Make the same circuit, but put switches A and B in parallel. That’s an OR gate.
In integrated circuits, we use transistors in stead of switches. They operate a lot like tiny electronically-controlled switches. And we make other logic gates besides AND and OR. And more complex things made of logic gates.
Putting lots and lots of them together with various gates’ outputs feeding the inputs of others, and those feeding the inputs of others, allows the construction of very complex logical computations. That’s how we build up very complex devices like microprocessors (CPUs). You can make binary digital logic gates do a lot of things if you are willing to use lots and lots of them.
An FPGA contains a lot of logic gates built up into standard groups. They also contain the equivalent of fuses which can allow those units to be configured and connected to each other in a variety of ways. Using those “fuses” and configuring the FPGA correctly, you can build up a custom circuit virtually of your choosing. A lot of stuff gets wasted, but it’s still a hell of a lot cheaper to make a small number of custom programmed FPGAs than it is to make truly custom-designed integrated circuits. It only becomes economical to make true custom ICs if you can sell a lot of them.
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