Monthly Archives: April 2021

ADDING CIRCUITS Addition is the most basic of arithmetic operations. Adding binary numbers is pretty much like adding decimal numbers, to add two numbers like 245 and 673, you break the problem down into simpler steps. Each step only requires adding a couple of decimal digits. In this example we would start with 5 plus 3 (etc.). Binary adders are combinatorial networks which receive n bits of the addends to be added as input and generate the bits of the binary sum with the relative carry as output. It is, therefore, a typical example of a combinatorial network with [...]

MULTIPLEXER DEFINITION The Multiplexer, also called MUX , is a combinatorial digital circuit able to select one of 2n input lines (data lines) and to report the values ​​of this line on a single output. For this purpose, in general, the circuit has, in addition to the data inputs, also n selection inputs. The figure below shows the simple block diagram of a MUX with 2 data inputs and 1 selection input. AND' a data line selector able to select different input signals both analog and digital. Once selected, the signals are collected and sent to a single output [...]

DEMULTIPLEXER DEFINITION A demultiplexer (or demux) is a device that takes a single line of input and routes it to one of several digital output lines. A demux of 2 n outputs has n select lines, which are used to select which output line to send input to. A demux is also called a data distributor. Demuxes can be used to implement general purpose logic. By setting the input to true, the demux acts like a decoder. DEMULTIPLEXER OPERATION The operation is similar to the MUX, both as regards the selection and as regards the activation of the AND [...]

MULTIVIBRATORS Multivibrators are circuits suitable for supplying square, rectangular and impulsive waves. Made in various forms, with transistors, operational amplifiers, logic gates, integrated circuits, they are divided into astable, monostable and bistable: Astable Multivibrator: it is characterized by two states between which the multivibrator oscillates without the need for external commands. The astable is a real generator of square and rectangular waves. Monostable : also called one-shot, this multivibrator has a stable state, in which it can remain indefinitely, and a quasi-stable state. By means of an input command signal (trigger signal) it is possible to switch the monostable [...]

MONOSTABLE CIRCUIT A monostable multivibrator can be used as circuit delay. Such a circuit it can receive a very fast signal as input and produce a signal with a well-determined active time as output . Think of the lights on the stairs of an apartment building. After being triggered by a switch, the lights remain on for a period of time set by the timer. It is possible to create a monostable both in positive and negative logic, ie which responds with a logic level 0 or 1 at the output and activated by the same logic at the [...]

THE LATCHES Combinational circuits are characterized by the fact that the output is the logical result of the signals present at the input at the same instant without considering propagation delays. A sequential circuit, on the other hand, also stores the previously assumed states in addition to those currently present at the input . There is a feedback which sends the output signal towards the input . In this type of circuit there is a memorization mechanism of the previous states which condition the following ones. These stored states are called internal variables, and the ability of a sequential [...]

TIMED LOGIC In wider contexts when digital circuits have to communicate with each other, it is necessary to synchronize the data transfer, also considering the delays that a given circuit can produce. This synchronization or clock is generally obtained by an astable multivibrator which, as we have seen, has no stable state but oscillates by means of RC circuits, producing a square or rectangular wave output. In microprocessors, synchronization is based on quartz circuits, they offer greater stability and much higher working frequencies. EDGE TRIGGED So far we have seen how digital circuits are activated by two reference voltages, [...]

ELECTRONIC COUNTERS INTRODUCTION Electronic counters are made using a chain of flip-flops with NET (Negative Edge Trigged) clock inputs. Based on the number of stages used, the set of outputs for example QA, QB, Qn produces at each clock pulse a binary number equivalent to the number of pulses received. A three-stage counter is called an 8 module as it is able to count from 0 to 7 23 = 8. The binary numbering obtained at the flip-flop output must be interpreted from left to right, that is Qn, QB, QA where the output of the first QA is [...]

7-SEGMENT DISPLAY One way to visualize the numbers is through this type of display where every access led in the right combination makes the decimal number appear. Each segment of the display is an LED along with a limiting resistor. There are two large types of 7-segment displays, those with common anode (AC) and those with common cathode (CC). 7-SEGMENT BCD DECODING To be able to read a number, so-called decoders are used, in particular in our case a "BCD-7 Segments" decoder which converts the binary input into a combination of seven outputs that turn on [...]