We have already commented on you previously, through the article “How is the material designed? This is how design engineers work»The tools used today for material design. In this article, however, we will introduce you to what logic gates are and the products of their combination, combination, and sequential systems.
What are logic gates?
Logic gates are combinations of transistors which are the minimum units to build any semiconductor, we are already talking about the construction of a memory, whether volatile or non-volatile, as well as any type of processor . So any semiconductor found in a computer is of the type made up of logic gates, even the microcontroller that controls your kitchen refrigerator is made up of logic gates.
All logic gates have a number of inputs and a single output and are responsible for performing a specific operation on the input data on the pins. In each pin a binary pulse is output, because it can only have two values which we call high or logical 1 or low or logical 0. Contrary to popular belief, a weak signal does not mean a signal without electricity but a signal with a lower voltage.
In order to better visualize logical zeros and ones mentally, think of them as a button, which has only two positions.
Types of logic gates
The logic gates used in the design of memories and processors are as follows:
- Puerta OR: the output will be a logical zero when at least one of the input pins of the OR gate has a 1. In the case where all input values are 0, the output value will be 0.
- Puerta AND: the output can only be logical if all input values are logical values. In all other cases, the output is always a logical zero.
- XOR gate: the output is logical when only one of the input pins receives a high signal and the rest is low, in the rest of the cases the output pulse will be low or logical zero.
- Investor: It’s not a logic gate, it just takes care of changing the signal up and down. It is used to create the inverted logic gates.
- NOR gate: is the inverse of the OR gate, the output will only be logical when all input signals are logical zero. Unlike the OR gate, the output will be logical zero if at least one of the input signals is high or logical.
- NAND gate: this is the inverse of the AND gate so the output will always be logical, unless all input values are logical, then the output will be logical zero.
- XNOR gate: is the inverted XOR gate. The output is a logic zero when at least one of the inputs is a logic input, under other conditions the output will always be a logic.
Combinatorial systems are nothing more than complex combinations of logic gates in which inputs and outputs are combined to make more complex circuits. An example of combinatorial systems are decoders, which convert the input signal to the selection of an output and which are used to access data in RAM memory or in the control unit of a processor. Another type of combinatorial circuits are the ALUs of the execution units of the CPUs and GPUs which are in charge of performing arithmetic operations with the input data.
We can divide combinatorial circuits into two different types:
- Elements used to perform arithmetic and logical operations.
- Elements that are used to transmit data such as multiplexers, demultiplexers, encoders, decoders, etc.
Unlike sequential systems, combinational systems do not operate on clock cycles and the output signal will be obtained “immediately”.
A sequential system is a combination of logical gates, but organized in such a way as to recall the past. With them you can create things like toggles and locks that can store information. Note, the registers of a processor consist of flip-flops.
Sequential systems need a clock signal to function, each given duration of which receives a high pulse, the clock speed being the inverse of the time of each cycle. (1 / hour of each cycle). For example, a 1 MHz processor goes from low to high 1 million times per second. A complex circuit can have multiple clock speeds and phases.
In order to visualize how a sequencing system works, imagine a group of people who are in one room and can only get to the next room when a whistle sounds, which is a clock cycle. Therefore, unlike combinatorial systems where the output is obtained in a single clock cycle, sequential systems operate in phases and the signal passes from one part of the circuit to another per clock cycle.