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50

They use a small backup battery, which you can read about on Wikipedia: Modern personal computer motherboards have a backup battery to run the real-time clock circuit and retain configuration memory while the system is turned off. In computers this is usually called the "BIOS battery" and is generally a lithium cell such as a CR2032. In the photo below ...


49

From the Reuter's article referenced: SARAJEVO, March 7 (Reuters) - European power grid lobby ENTSO-E urged Serbia and Kosovo to urgently resolve a dispute over their power grid, which has affected the broader European network, causing some digital clocks on the continent to lose time. Figure 1. The ENTSO-E System Operations Committee has 5 permanent ...


47

Clock errors are not corrected, they are compensated in two steps. 1. Error determination The GPS control segment uses reference receivers in well known locations to determine the actual orbital elements and the clock error of space vehicles. The reference for position is the WGS84 reference frame, for time it is the international atomic time. Even the ...


36

An illustrative example or two may help here. Take a look at the following hypothetical circuit: simulate this circuit – Schematic created using CircuitLab Suppose to start both A and B are high (1). The output of the AND is therefore 1, and since both inputs to the XOR are 1, the output is 0. Logic elements don't change their state instantly - ...


36

I guess the confusion is you assume you can only send one bit per clock cycle. There are lots of ways a communication scheme can essentially encode more than one bit per symbol. A symbol is abstract idea as the atom of transfer in a communication system. It's really too big of a topic to cover in an answer to this question in any depth, but imagine you ...


34

Clocks are used in computers for the simple reason that most if not all of the circuity is synchronous sequential logic. In a synchronous circuit, an electronic oscillator called a clock generates a sequence of repetitive pulses called the clock signal which is distributed to all the memory elements in the circuit. Now, that may not seem satisfying ...


34

How a decrease in electricity production can lead to a decrease of the frequency on the grid on the long term? Isn't the frequency a parameter controlled by the power plant at the end of the day? Answered before: Why do generators have to rotate at a slower frequency if demand outpaces the supply? If the loss of power from some countries causes a ...


34

With SDR, there are two clock edges per bit, but only at most one edge on the data line. With high frequency communication, the analog bandwidth limits how close you can put edges together on any given wire. If your clock signal hits that limit, you're wasting half of the bandwidth of the data wires. Therefore, DDR was invented so that all of the wires hit ...


30

Modern equipment often uses ultra-capacitors to keep real-time clock powered when the system is off: This is a typical solution for most mobile phones which are almost constantly powered and only need the back-up power when the user removes the battery.


26

While the other answers are definitely true: electronic devices cannot keep track of time without a power source, there are other considerations that can give the illusion of keeping track of time: connected devices ask for a time synchronisation as soon as they connect: computer usually gets it from the internet using NTP (network time protocol), GSM ...


25

I don't mean to rain on your wireless parade. You've ran into a tough but unexpected requirement. Something like that warrants re-evaluation of the whole system design. 1st thing that comes to mind is to clock both units off one oscillator. You have Bluetooth communication, which hints that the range is on the order of 10m. You could connect your units ...


23

Actually crystal oscillators can easily go up to 10's of MHz. Above that in most cases a PLL (Phase Locked Loop) is used, which is an oscillator that is not very accurate in itself, but can be tuned (its frequency can be adjusted somewhat). The frequency of this high-frequency oscillator is divided by a suitable factor (dividing a signal by a power of 2 is ...


23

This is done using a device called a phase-locked loop, or PLL. Here is a block diagram of a basic PLL: simulate this circuit – Schematic created using CircuitLab The oscillator on the motherboard does not run at the CPU clock frequency, instead it runs at a frequency on the order of 100 MHz. This oscillator serves only as a known, stable reference ...


22

Since the code snippet you're interested in isn't big, you could disassemble your compiled code, look at all the assembly instructions and count how many cycles they need. You can find the number of cycles for each instruction in the datasheet. If you have an oscilloscope, you can turn on a pin before the if statement and turn it off after your code snippet. ...


21

I feel a lot of these answers are not exactly hitting on the core question. The micro-controller has a clock simply because it executes (and is driven by) sequential logic. In digital circuit theory, sequential logic is a type of logic circuit whose output depends not only on the present value of its input signals but on the sequence of past inputs, the ...


19

How can a decrease in electricity production lead to a decrease of the frequency on the grid on the long term? Isn't the frequency a parameter controlled by the power plant at the end of the day? You can think of the electricity grid as being like a giant mechanism. Induction motors are like belts that can slip a bit. Synchronous motors and generators are ...


19

The real problem is bandwidth. The highest frequency that a data line can generate (well, not counting slew rate) is when it's sending a 101010 data pattern, which occurs at half of the data rate. With single data rate (SDR) transmission, the clock produces one complete cycle for each data bit, hence running at double the frequency of what you might see on a ...


19

32kHz ultra low power oscillator: Used for RTCs (Real-time-clock). These can run in the background and enable time-keeping, even when the controller core is sleeping. This enables to have a running clock without the high power consumption of the controller core. The 32kHz oscillators are pretty precise and typically have an error of less than a minute per ...


18

If the flip-flop's setup time is 20 ns, it means that data has to be stable atleast 20ns before the capturing clock-edge. Similarly hold time is the amount of time, data has to remain stable after a clock edge has appeared. So together they define a "setup-hold-window", in which data has to remain stable. If the data changes/toggles within this window, the ...


18

Yes. Kind of, at least. As you're coming from a wired background, I'll build the analogy from there: Where UART only works because receiver and transmitter clocks are similar enough so that, for a short burst of bits, they don't drift apart, the same applies to wireless digital communications. If your symbol rate is low enough, and the receiver knows ...


17

What you need is a PLL, a phase-locked loop. It works by comparing one oscillator that you can control, with a reference oscillator. The trick is that it is easy to divide the frequency of an oscillator using a digital counter, so what you do here is to divide the 14.3 MHz oscillator by 143, the 10.0 MHz reference by 100, and then use the output from this ...


17

There is a line in the Parameters table on p.1 of the datasheet, which describes the function of the Tri-state. It's a kind of an enable-disable pin. If Tri-state pin is logic "1", then oscillator is connected to the output pin. Same happens if Tri-state is left unconnected (there's probably an internal pull-up). If Tri-state pin is logic "0", then ...


17

So, the first problem will be that you need to drive that long cable! A 1km long piece of wire is simply a large load, and your microcontroller output will have a hard time changing the voltage on that reliably. Think of the fact that the wire runs through its environment as a capacitor of wire to ground. So, you need a strong output driver. You want that ...


16

Short answer: managers want a simple, testable, PROOF of function before committing to millions (or more) dollars to a design. Current tools, just do not give asynchronous designs those answers. Microcomputers and microcontrollers typically utilize a clocking scheme to insure timing control. All process corners have to maintain timing across all voltage, ...


16

A GPS receiver creates a local replica of something called "GPS system time", which is a virtual timebase created from all of the clocks on the satellites and ground stations. This replica is integral to the process of coming up with a navigation solution, which is based on measuring the signal delay from each satellite to an accuracy on the order of ...


15

You really need to think hard about what you really mean by "simultaneous". Over a span of 1000 meters, the concept does not extend down to the sub-ns regime. Heck, it would take a light pulse more than 3000 ns to traverse that distance, and an electrical pulse would take more like 5000 ns over an ideal transmission line. Your unshielded wire is going to be ...


14

The LTC1799 can be programmed by a resistor and a link to produce a vast array of frequencies. Is there a small (6-pin) DIP I can use to generate multi-MHz squarewave clocks with an external crystal? It's certainly small It's 5 pins not 6 It's not DIP but you want "small" and DIPs are not small in comparison to SM devices. It doesn't use a crystal


14

In the video the circuit worked as if the negative pulses were nonexistent. Yes, that effect is due to the chip. Let's have a look at the SN74LS08's datasheet and look at the circuits on the chip: Notice the two Schottky diodes between the inputs A and B and GND. These diodes are needed to protect the sensitive transistors in the chip. Nearly all chips ...


14

Let's do it! Say we have the code int main(void) { volatile uint8_t val = 0; while (1) { if ((PIND & (1 << PIND6)) == (1 << PIND6)) { val = 1; } else { val = 0; } } } Say we use AVR GCC with optimization flag -O1, then the disassembly of the relevant section looks like this: ...


13

Yes, you can stop the clock completely and restart it at a later time without consequences. You could even replace the clock by a pushbutton and go through your program literally step by step (frequency: about 0.1 Hz). Power is almost linear with frequency: at 10 MHz the microcontroller will consume 10 times as much power as at 1 MHz. This does not mean ...


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