Questions tagged [clock]

A digital signal that goes high and low at a specific frequency.

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37
votes
4answers
11k views

How to synchronize two microcontrollers to micro-second accuracy?

I need to synchronize two micro-controllers so that they can measure the speed of propagating waves. The time delay measurements need have microsecond accuracy (error less that 1/2 of a microsecond). ...
29
votes
6answers
14k views

How precise is the frequency of the AC electricity network?

If I make a digital clock which first detects the AC frequency roughly (whether it is 50, 60, 100Hz, etc), then uses it as its clock pulse source, how precise would it be? Would it work world wide ...
18
votes
5answers
29k views

Why edge triggering is preferred over level triggering?

I am trying to understand why edge triggering is preferred over level triggering. In my book it is not explained clearly. After searching online I came to know that edge triggering is insensitive to ...
15
votes
2answers
8k views

How can a CPU dynamically change its clock frequency?

My Intel CPU changes clock speed depending on the usage, but how does it decide what clock speed to run at? Is the clock speed determined by the OS software using an algorithm, or is it hardware based?...
3
votes
4answers
13k views

How to generate edge-triggered pulse

First, a bit of background: I am just a hobbyist with electronics and have very little formal education in the area. I understand most terminology, but generally require a schematic for me to be able ...
4
votes
3answers
5k views

Design practice crossing clock domains and async signals

I have been designing a few projects on different FPGA's in VHDL, and it seems my most common source of "hard to find errors" is when I forget to synchronize an async signal, or forgets to resync a ...
1
vote
3answers
2k views

RC circuit as clock source

I am not understanding something very fundamental here , I have read that an RC circuit can be used as a clock source. From this I assume a DC input. Playing around with my oscilloscope the only time ...
2
votes
4answers
4k views

Edge triggering seems to me leaving every circuit in an inconsistent state?

I was informed on this forum that edge triggering could be a solution for multiple propagation in a circuit with feedback (the output wired back to the input). But to me edge triggering seems to ...
67
votes
5answers
12k views

Serbia, Kosovo power grid row delays European clocks. Why?

According to this article (and a lot more published today on the same topic), Kosovo electricity net production balance has decreased during the last weeks. This has led to a small deviation of the ...
5
votes
3answers
32k views

How to calculate the time of one single tick on microcontroller

I have been in Embedded system for 8 months. I have worked application part more compare with low level. I have basic questions on systems ticks, How to calculate the system tick of Timer, if I am ...
5
votes
1answer
3k views

Real-time clock and Crystal precision

I want to use a crystal as the base clock for a watch. Most reference designs I could find use a 32.768 kHz crystal at 20 ppm (parts per million) precision. According to my calculations, this leads to ...
5
votes
2answers
822 views

How to get 8MHz square signal out a pic18f45

I am using a Pic18F45K40 to control an ST7590 power line networking chip which requires an 8MHz clock signal to function. I read the datasheet and it looks like a 16MHz signal can be generated from ...
5
votes
2answers
3k views

Does the internal 8Mhz oscillator in an ATTINY run even if no clocks are connected to it?

If I set up the fuses on an ATTINY so that the system clock uses the internal 128Khz oscillator (sometimes called the "Watchdog oscillator"), does the internal 8Mhz oscillator still run? It does not ...
1
vote
2answers
1k views

Counter in verilog

i want to make a counter that increases by the value of its inputs, but i did the testbench and the output is undetermined, xxxx. Can someone tell me if there is something wrong in this code? ...
1
vote
0answers
202 views

STM32F4 OC Clock Jitter

I am using STM32CubeMX to configure an STM32F4 to output a clock signal using Timer 3, Channel 4 on PC9. I have read in the datasheet PLL section that jitter shouldn't be more than 15ps RMS but I am ...
103
votes
5answers
8k views

Can microcontrollers be run at arbitrarily low clock frequencies?

The datasheet for the ATTiny13A, for instance, lists Min frequency of 0 MHz. Does this mean the clock can be run at any arbitrarily low frequency with no ill effects? I'm assuming it draws lower ...
40
votes
3answers
8k views

How do GPS satellites refresh their clocks

How do GPS satellites keep their on board clocks accurate? I assume that they need to get update from a base station. But how do you make sure that after the update all the satellites are synchronized,...
9
votes
3answers
2k views

Routing 30MHz clock thru several boards

I'm using TLC5945 LED driver. Microcontroller (I'm using LPC1343) must provide a clock for it's internal PWM timer/counter. Maximum allowed clock speed is specified as 30MHz. I will have several ...
10
votes
3answers
28k views

What is clock skew, and why can it be negative?

My HDL compiler (Quartus II) generates timing reports. In it, the nodes have "clock skew" column. The only definition of clock skew I found is in the TimeQuest documentation (see page 7-24): To ...
9
votes
6answers
2k views

1 kHz clock over long wire

I will have a wire that will run up to 1000 m with many nodes connected to it. The wire will run along a CAN bus and a ground wire and must transport a 1 kHz square wave 50% duty-cycle clock signal to ...
17
votes
6answers
29k views

Using the ATMega328 with the internal oscillator?

I have a project that I think would be best suited for an ATMega328P. However, in every simple project I've seen, people always hook up a 16MHz external oscillator. From what I can see, it should have ...
7
votes
2answers
8k views

What is the best way to layout a PCB with crystal oscillators and MCU?

I have heard that the clock circuit is a noise source and that the clock circuit is also sensitive to noise. I believe that keeping the clock circuit close to the MCU and keeping other routes or ...
6
votes
1answer
13k views

Why use STM32 HSE?

Why do we use an external oscillator for STM32??? Why not just use the microchip oscillator? I am using STM32F2xx it clocks at 120Mhz But, an external oscillator of 12Mhz is latch into the microchip,...
6
votes
6answers
4k views

How to build an ultra-low power time counter?

Inspired by this question I would like to know how low power you could go with a counter + 32 kHz oscillator (possibly made by yourself). I found a nice oscillator circuit on a BJT reportedly drawing ...
10
votes
2answers
4k views

Sharing an oscillator between two ICs

I have a microcontroller and an FPGA on the same board. If they're both going to run at the same clock speed, can I just use one oscillator to clock them both? There seems like there is something I ...
6
votes
1answer
9k views

ASIC timing constraints via SDC: How to correctly specify a ripple-divided clock?

Introduction Having found multiple, sometimes conflicting or incomplete information on the internet and in some training classes about how to create timing constraints in SDC format correctly, I'd ...
2
votes
1answer
31k views

Divide clock frequency by 3 with 50% duty cycle by using a Karnaugh Map?

In this document, On semiconductor describe how to design a divide by 3 system using a Karnaugh Map: ...
8
votes
2answers
1k views

Is it true that the power line frequency is kept accurate by atomic clocks?

I've heard rumors that the power line frequency is kept stable and accurate by syncing it with atomic clocks. Is this true? What kind of accuracy does it have? Is this true everywhere?
4
votes
3answers
5k views

Stopping the clock without gating the clock

How would one go about making a shift register which only shifts when an enable line is high? The obvious answer is to pass the clock and enable through an AND gate, but that breaks the "don't gate ...
3
votes
2answers
495 views

How to “deserialize” a digital output to 4 digital outputs

I am working on a small test project for my Arduino and as part of it, I want to display a number on a 7-segment LED system. My first setup involved just direct links to the 7-segment display and ...
3
votes
1answer
470 views

Random clock Generation with unequal 1s and 0s distribution?

We need a pseudo-random clock with a length N, in such a way that out of every N clock pulses, ...
10
votes
2answers
5k views

ASIC timing constraints via SDC: How to correctly specify a multiplexed clock?

Introduction Having found multiple, sometimes conflicting or incomplete information on the internet and in some training classes about how to create timing constraints in SDC format correctly, I'd ...
7
votes
1answer
3k views

Why does this rising edge detector using a capacitor and a resistor work?

So in this video from Ben Eater he makes a rising edge detector using a capacitor and a resistor like the one below. simulate this circuit – Schematic created using CircuitLab In the video Ben ...
6
votes
3answers
2k views

Crystal circuit works in breadboard but not in perfboard

I'm a beginner and I'm trying to build a digital clock. My clock generator looks like this: circuit http://img189.imageshack.us/img189/855/tempgd.png It works perfectly on the breadboard, where I ...
6
votes
2answers
1k views

Reflection on SPI Clock Signal, termination or stub issue?

This is a SPI Clock. 6.25MHz frequency. I see something like a reflection. I don't think it's from cross talk on my board from another signal, not sure. Added as requested: This is my system diagram (...
3
votes
1answer
178 views

Synchronising GPIO transitions to an external clock

Currently, I am using an ADC with an external trigger with the caveat that the edge of the trigger must be within +/- 25ns of the ADC's clock (See Figure 3 of the datasheet). The ADC's clock is ...
3
votes
2answers
270 views

Crystals, capacitors and W5100

Background: I have built a number of devices based on the W5100 chip, all them were (are) working more or less decently. However last batch currently in testing show faulty behavior - almost all of ...
2
votes
3answers
2k views

Capacitive load - Matching Right Crystal and Caps for oscillator circuit - DS1302 RTC - cut and trim

CL = (C1 * C2) / (C1 + C2) + Cstray I have a 12.5pf crystal. DS1302 is happy with 6pf. what is trim capacitors to make him happy using 12.5pf? 12.5-6=6.5pf (6.5*6.5) / (6.5+6.5) + cstray= 3.25pf + ...
1
vote
3answers
9k views

Clock divider VHDL

I created a clock divider with the code below. i followed steps in prof chu's book. ...
1
vote
1answer
2k views

Genlock two OV5642 camera modules on Arduino with ArduCam

I need to shoot stereo video or stills at about 10 FPS possibly in perfect sync. My plan is to set up a 3D stereo rig (2 standalone units - each consisting of Arduino UNO + ArduCam shield + OV5642 ...
1
vote
2answers
115 views

Create a pulse that is active from ~0.3 to 0.4 times the clock period

I'm sorry if the phrasing is somewhat weird, but the question is hard to articulate. I've created an IC Sample-and-Hold where I have a hold capacitor at the output. I want to charge this capacitor ...
0
votes
1answer
362 views

How can I turn a clock signal into a logic high that also goes low when the clock drops out?

I have a differential clock signal coming from an IC. If the signal is present, I need a TTL "high" to enable a high-side FET driver. When certain conditions are violated, the IC will send the ...
0
votes
1answer
1k views

State switches in FSM

I have a simple board with 6 buttons, consisting of 3 columns and 2 rows I would like to detect the pressed button. My code below works with this fsm: ...
0
votes
1answer
135 views

Controlling the frequency of oscillation of SI530 VCXO

I am thinking of using the SI530 VCXO as a means to generate clock signal at frequency of 1.4 GHz. But in the datasheet I do not pin which controls the frequency of oscillation. Can someone help! ...
-3
votes
3answers
2k views

Generation of clock signals

Inside a computer, a crystal oscillator sends signals to a microcontroller or microprocessors. I want to know if the crystal oscillator is increasing the frequency or generating pulses. My questions ...
4
votes
2answers
668 views

Square wave generator has nigh-useless output

I have a system that was designed for testing digital components. I have a device in the system which is used for generation and acquisition of digital signals. Now, I will happily admit to not ...
3
votes
3answers
633 views

Detection of simultaneous edges of two asynchronous clocks

This question was initially asked at StackOverflow as a Verilog question, but, eventually, it became more hardware than software discussion. The question: how simultaneous (positive) edges of two ...
3
votes
2answers
4k views

Introduce delay on a single bit signal w.r.t. input clock

I have seen this question and removed the "#.." part of my code to introduce delay, since my code will ultimately run on hardware. Anyway, I am trying with counters and not able to introduce the ...
2
votes
2answers
329 views

10 MHz reference distribution (daisy chaining vs. BNC tees vs something else)

10 MHz is the quasi-standard for reference clock in measurement equipment. Most boxes have "REF in" and "REF out" or "10 MHz in"/"10 MHz out". In my case, I have a measurement setup consisting of an ...
2
votes
1answer
2k views

Circuit to enable (inverted) clock glitch free

This is a follow-up question to https://electronics.stackexchange.com/a/95195/13354, in which I was asking about a specific solution to the more general problem described here. I'd like to create a ...