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Questions tagged [digital-logic]

Digital electronics treats discrete signals, unlike analog electronics that treat continuous signals. Digital logic is used to perform arithmetic operations with electric signals, and constitutes the base for building CPUs.

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74 views

Raw programming of an Altera FPGA

I have an Altera Cyclone IV FPGA (for ie) and my question is: is it possible a raw programming of the FPGA? Is it possible to set "manually" the gates for making experiments? Thank you
57 views

When should we NOT simplify a digital signal in an expression?

When we do a simplification in a Boolean expression, sometimes we eradicate some Boolean variables, either from part of the expression or entirely if it's not needed. Is there a case in digital design ...
71 views

Is it better to combine logic for two flip flops in a single always block?

I have always used separate always block for infering different flip flops when they dont have much in common. ...
181 views

Is this circuit from a textbook wrong?

(This is not a homework question.) While reading "Digital Computer Electronics" by Albert P. Malvino, I found this circuit on page 121, figure 8-22(a). It claims to be an example of a discrete TTL ...
91 views

Can the output of one logic gate serve as input to more than one subsequent logic gates?

NOT gates take one input, AND and OR gates take two inputs. But can any gate have more than one output? I've only ever seen diagrams where each logic gate has exactly one line coming out the right end....
11 views

Symmetric Inverter Sizing Based on load capacitance and propagation delay

I am doing Symmetric Inverter Sizing Based on load capacitance and propagation delay that is given. Also mobilities, threshold voltages are given. Symmetry ratio is process dependent based on ...
59 views

2-Bit timer with 1 ms period

I am trying to find a simple hardware solution to implement a 2-bit timer that gives out 2-bits continuously repeating data 00, 01, 10, 11, 00, 01.... whose time period is approx 1ms. The accuracy and ...
73 views

Designing a cryptographic S-Box in Logisim

I am currently working in Logisim and was wondering if I can design some ciphers in the same. One such cipher is PRESENT cipher which is essentially a block cipher. I did get that I need to design the ...
71 views

How do I calculate rise times for a push pull GPIO with load?

simulate this circuit – Schematic created using CircuitLab This is a simplified example of a push pull GPIO found in most microprocessors, with a load attached. Using the capacitance and ...
64 views

ESD SPI/ISP bus protection

I am designing a board based on the Atmega328P microcontroller. For this controller there is an ISP connector for programming. This connector has the following pins: MOSI / MISO / RST / SCK. There is ...
3k views

How should I understand FPGA architecture? [closed]

I've been given the task to make a 2-bit adder by programming a FPGA. The FPGA is seen below: However, I don't even know how to begin this task, because I don't understand what I am looking at. ...
18 views

Eport E20 JSON HTTP POSTING FORMAT [closed]

I want to post to my web application by using a Eport E20 ethernet Module Eport Website with a HTTP post JSON format. I have connected the device directly to my laptop using a serial terminal. I was ...
63 views

How to get a 1 clock period pulse from a constant input? [duplicate]

I want to make a digital circuit that produces a pulse 1 clock period in duration whenever I see the input to the circuit go HIGH. I only have a flip-flop, an AND-gate, and an inverter. How do I ...
114 views

How does a cpu represent bits? [closed]

Maybe my question was asked earlier, but I want info away from logical abstractions, in different contrast. START: A transistor can represent two states - on and off - means 1 and 0 - means 1bit. So ...
83 views

How to construct a discrete circuit to send out a square wave with N pulses?

I want to build a simple and discrete circuit (without any integrated circuits) which puts out a square wave (50:50 duty cycle) with N pulses (rising edges)? For example for N=4 the output should ...
80 views

Driving NPN with Raspberry Pi

When driving an NPN transistor using the GPIO output on a raspberry pi I assume no protection is needed on the GPIO side of the circuit? So nothing would really be needed beyond this to drive the ...
57 views

microcontroller serial communication noisy on direct wire connection

I did a simple circuit to test data communication between two separate microcontroller circuits. The big X is actually two wires (not touching each other) that connects the two circuits together. ...
86 views

Is it possible to make an SR latch using XOR gates only?

Due to certain rules, I can only use components available to me, so I cannot implement an SR latch using the standard NOR or NAND configurations readily available online. If it is possible, please may ...
26 views

4 bit synchronous binary counter using T flip-flops

I'm trying to make a 4 bit synchronous counter using T FF. I managed to draw the excitation table and evaluated the functions but I'm unsure what the pin configurations will be. I tried connecting the ...
44 views

Sum-of-Product understanding

I am trying to learn Sum-of-Products and minterms and maxterms for logic design, but I don't know how the book gets the f(x1,x2,x3) part. I think I understand the minterm from the first pic (it's ...
55 views

Verilog: negative value in brackets of vector signal definition

I am looking at the code in the following website. https://www.csee.umbc.edu/~tinoosh/cmpe641/slides/05-Memories.pdf In their code, they claims something like input signed [7:-12] c_in; I am ...
74 views

The Pin 1 Problem in Audio, Star and Mesh Ground, and Contradictory Grouding Practices in Audio and Digital Systems

I recently came across the concept of "Pin 1 Problem" known in the pro-audio electronics. It seems straightforward at first, but becomes confusing when it comes to grounding. Let me describe the ...
166 views

How do I efficiently search for ICs? [closed]

I am a computer engineering student with an electronics background (i.e. mandatory circuit design and analog electronic courses) and my degree thesis requires me to design an electronics project. So ...
29 views

What is meant by taking dual of a boolean expression?

I read online that if we have a set of SOP terms giving a boolean expression, then the POS terms of the complement of the SOP terms will give the same expression. POS(f)=SOP(f'). This is called ...
48 views

If a 4-bit binary digit in 2's Complement form is stored in 8 bits how is it represented?

I am quite new to Digital Logic. I got this doubt while solving a problem. If a 4 bit binary digit in 2's complement e.g. X3 X2 X1 X0 is stored in an 8 bit space what will be the representation in ...
32 views

Expected output of DFF_2 if DFF_1 has hold violation

I am trying to figure out the output of flop DFF_2 when If DFF_1 has hold violation. My answer - DFF_2(Q) = X If DFF_2 has hold violation. My answer - DFF_2(Q) = X I understand the FF's go to meta-...
116 views

RS485 Eye diagram - does it look good?

I got a new diff probe, I am trying it out on RS485. I'm triggering on the rising edge. The RS485 is running at 25Mhz. Does the eye diagram look good? Could I double the speed (50MHz) and be ok? (...
70 views

Problem with state machine that calculates the Greatest Common Divisor in VHDL

I am supposed to implement the greatest common divisor in VHDL. The testbench and the interface were provided. However, every time I run the simulation, this thing gets stuck in state 6 (...
566 views

What does the triangle look like in this diagram?

Using my intuition, I would assume the triangle in this simple circuit to be an inverter, but does that look correct? What is this symbol?
109 views

How many ALUs (and threads) are in a Pentium CPU?

I'm reading a book bottom up where it said: The Arithmetic Logic Unit (ALU) is the heart of the CPU operation. It takes values in registers and performs any of the multitude of operations the ...
79 views

Equivalent resistance in this mosfet circuit

simulate this circuit – Schematic created using CircuitLab I have 3 NMOS are connected as shown above. I need to calculate equivalent resistance as seen by the capacitor so that I am able to ...
146 views

The TI quad-XOR gate acts as it is short circuit

I have a TEXAS INSTRUMENTS CD4030BE Quad Exclusive-OR gate. I have an electronic board of simulate this circuit – Schematic created using CircuitLab using this and this refrence. According to ...
101 views

Trying to simplify a Boolean expression

Simplify the following expression using Boolean Algebra: $$x = \bar{A} \bar{B} \bar{C} + \bar{A}BC + ABC + A \bar{B} \bar{C} + A \bar{B} C$$ Answer: \begin{align*} x &= \bar{A} \bar{B} \bar{C} +...
26 views

Boolean Expression Minimization Question

How does one simplify this expression further? f(a,b,c,d) = a'b' + b'c' + b'd' + a'cd' + bcd The simplest form is f(a,b,c,d) = a'c + b'c' +b'd' + bcd I've been staring at it for a while and I don'...
48 views

Synchronous Up/Down counter which shows given sequence simultaneously on 5 x 7-segment displays

I was given a project to design a Synchronous Up/Down counter which displays my sequence (2,1,0,6,5) on 5 x 7-segment displays simultaneously. I started first by designing the Up/Down counter and ...
41 views

How to specify a state when the system does not change in an ASM chart

This may be simple or obvious but I have not found any definite solution by googling. I want to include a state in my Algorithmic State Machine chart were nothing changes (no operations on registers) ...
103 views

Understanding of a W65C02 micro computer

I found a tutorial with a schematic where you can buy a PCB for an old computer with a 6502 microprocessor. I want to do this on my own with my own PCB (but I test the circuit on my breadboard first) ...
71 views

Flip flop asynchronous reset timing

Let's say you unassert an asynchronous reset signal to a flip flop after you need to to meet setup timing but before the positive edge of the clock. You're in trouble right? Now let's say you've got ...
59 views

Need to concatenate 1 bit of a 2nd data with every new 1st data

I have two different datas. 1st data keeps coming in chunks every cycle (fixed width; new data comes in every cycle) 2nd data is fixed and needs to be appended 1 bit every cycle (fixed width and fixed ...
49 views

Voltage controlled connection of two signals that are at higher voltage than the control voltage

Given are two signals A and B. I want to control the connection between them by a signal C. However, signal C is a logic signal with a voltage of 3.3V for high and 0V for low whereas signals A and B ...
42 views

What happens when you assign the result of a reduction operator to a multi-bit wire?

I may just be having a mental breakdown, but what should be the value of 'f' after the following: `Verilog wire [3:0] u = 4'b0101; wire [3:0] f = |u; Should ...
59 views

A logic board with two inputs where the state of the output changes upon changes in any of the inputs

Sorry if my question if very novice. I want to have a simple logic circuitry with two inputs and one output. The state of the output should change if the state of any of the input changes. The inputs ...
114 views

What is meaning of active low input in combinational logic circuits?

I am currently doing self study on combinational logic circuits. I encountered few terms like active low output, active low input. I understood what active low output means (putting not gates at ...
658 views

Crystal Oscillators in MCU

let's consider a MCU (for instance ATMEGA328) with a crystal. I know that the electrical model of a crystal is this one: My question is: which is the circuit that makes it oscillate? I do not see it ...
4k views

Why do we need to use transistors when building an OR gate?

Why do we need to use transistors when building an OR gate? Wouldn't we be able to achieve the same result without transistors at all, just by joining the two ...
69 views

Toggle circuit with 1 x NAND, OR, and NOT gates?

I am sure there is a more specific name than "toggle circuit". I am simplifying a schematic. To do so I have replaced a larger circuit with one much smaller, but in doing so, I have lost the 74*74 ...
45 views

PWM frequency and sine waveform generation

I am trying to follow some guides (for instance this) to generate some analog signals (for instance a sine wave of 50 Hz) with Arduino (but my questions are general). But I have two basic questions: ...
66 views

Verilog Code for this (simple) Logic Gate?

Here's as far as I've gotten with this: ...