# Tag Info

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 ...

11

What these are for: 32kHz low power: "digital watch" crystal. Use this when you want to power down the main oscillator but not lose track of what time it is so you can wake up periodically. 32kHz RC: cheaper (no crystal), but less accurate. When you want a digital watch that doesn't tell the correct time. external fast crystal: for things like ...

10

When there is a 90° phase shift between two 5MHz clocks, that means there is a 50ns skew between them. If you divide those two clocks by 5000000 using two instances of the same counter structure, you'll get two 1Hz signals with 50ns skew between them (which is roughly 0° at 1Hz). I doubt you can see this with bare eyes. So to me, this test gives you no ...

9

Learning Verilog is one thing. It also good to learn digital design. Modern designs use clocks. The synthesis tool doesn't want to make something sensitive to two different edges. You should us a clock and either count or reset depending on the input. You should digitally detect the edge to count up. always @(posedge clock) begin KEY3_d1 <= KEY[...

8

The "Good News" first: I can save you using an online calculator. "ppm" is for "parts per million"; so 50 ppm simply means a relative error of 50·10⁻⁶; at 200 MHz, that means 200·10⁶ Hz · 50·10⁻⁶ = 10000 Hz. It's that simple! Bad news: Doesn't have anything to do with jitter. Your clock could be running at, say 200.010 MHz (...

8

They are not strictly necessary but the vendor is attempting to cover as many use-cases with one part as they can. Some applications may want to use the internal oscillator, others may need a precise clock source, others may want low power consumption. Generally you will use only one in a specific design although in some cases the clock mode is changed ...

7

This is related to a feature of the IIC protocol called clock stretching. If a peripheral device is unable to process data from the bus master in time (or prepare its output to be transmitted back to the master), it will continue hold the SCL line low (remember that it is open-drain, so there is no bus contention), until it is ready for transmission to ...

7

To avoid the possibility of the glitch, you might consider making the read signal a registered output. This will require some redesign of your state machine, since if you simply put a register in front of your AND gate, the read pulse will occur almost one clock cycle later than without the register. Therefore you will have to change the fan-in to your AND ...

7

Here is the clock configuration in block-diagram form from ST's configuration tool (STM32F103). As you can see, there are internal oscillators and two oscillators that use external frequency-determining components (crystals or resonators typically). I have this configured to use an external 8MHz crystal and a 32.768 kHz watch crystal. I could have used the ...

6

The 74LS273 is a D-type flip-flop which won't toggle. You need to use J-K flip-flops (74LS73 or 74LS76) in toggle mode, i.e. J and K tied together and pulled high. The output register can be a J-K flip-flop operating in D-type mode, i.e. using a NOT gate so that K equals not J. Or it can be a dedicated D-type (74LS273). Something like this synchronous ...

6

Here's a good clue: - And, if you look at the value for $t_4$ it is quoted here: - So, a new data bit is available between 0 and 40 ns of the falling edge of SCLK. This means you can't rely on the falling edge of SCLK to read valid data. Of course, if you look at $t_7$ it tells you that current data is valid for maybe 7 ns should you attempt to read it ...

6

The clock input pins have optimised routes to the clock distribution logic. At worst this means lower delays compared to general purpose pins. At best this means accurately constrained delays, that allow the clock PLLs to drive the clock nets with near zero skew from the clock input pins. The tools generally don't forbid a design that uses GP pins as clock ...

5

The problem is statements: if(rising_edge(Set_Button) and Set_Button = '1') . . if(rising_edge(Enable_Button) and Enable_Button = '1') When you synthesise this code, the synthesiser recognises these two signals as the clocks in your design. These are also Input Ports in your module. If these signals were truly clock inputs in your design (which I don't ...

5

There (was) an IC for that: https://www.renesas.com/us/en/general-parts/1523-video-clock-synthesizer-i2c-programmable-delay. Obsolete now... no thanks to Renesas. Basically, multiply up by 455 to get 2fsc or 910 to get 4fsc (that is 14.31818MHz.) The latter is available as a crystal. Another option is to 'crash lock' a crystal oscillator to regenerate the ...

5

yes. A square/rectangle wave is required. not necessarily. For example a base model 8051 microcontroller divides the oscillator frequency by 12. Thus the counter/timer clock is oscillator/12. Compare this with an AVR mega328 - The default internal oscillator is 8MHz and assuming the div8 fuse is not enabled, then the timers can count at 8MHz. There's ...

5

Asynchronous delays are effectively impossible in FPGAs. Running off anything but the system clock as a clock is fraught with difficulty. The correct way to do it, and by correct I mean a way that the timing and PAR tools will work with you rather than you having to fight them, is to use a system wide high speed clock, and use clock enables to qualify when ...

5

Yes, that's the standard representation of a buffer. What you see are clock buffers which are present there to not degrade the rise and fall times of the clock. As typically clock nets have high fan-out, you need high drive strength to ensure that a nice square wave reaches all the registers. And yes, it introduces a delay in that path. For instance, in your ...

4

No two clocks will ever perfectly match. The method of determining the true clock frequency from the data is called "clock recovery". If you know the nominal bit rate, then one straightforward method that doesn't require use of a PLL/DCM block is to over-sample the data and look for edges. Normally you would need to over sample by at least 4X ...

4

On many electronic designs transmission line effects do not need to be considered until about 40MHz or 50MHz. For a 1.28MHz signal, a transmission line is most likely not needed. The wavelength is over 200m so unless the cabling system is on that scale, reflections and ringing are not likely to be noticeable. This means if you use high impedance as a clock ...

4

Assuming: KEY input is already de-bounced Your board has flip-flops with asynchronous set/reset No other edge events will be added Then you could do this: always @(negedge KEY[3], negedge KEY[2]) begin if (!KEY[2]) begin // async reset mSEG7_DIG <= 0; end else begin // synchronous add mSEG7_DIG <= mSEG7_DIG + 1; end end However the ...

4

Edge triggered FFs have set-up and hold time requirements. Only data that was present before the clock triggered, will have satisfied the set-up time, and thus be "registered". Since (if well designed) the FFs have their clocks triggered at the same time, or nearly the same time, data that is "registered" at the input of one FF will ...

4

To understand it, consider first a gated D-Latch which is level sensitive which means that the input is applied to the output as long as the gate (E) is active, otherwise the last state is maintained: Now one way to implement an edge triggered D-FlipFlop is by using two D-Latches in a master-slave configuration: When the clock is low the first latch (the ...

4

That division operation works fine fine. It just treats everything as a truncated integer. However, be aware The clock is not a regular signal that runs through the logic fabric. Clock signals on FPGAs are distributed through one of the clock distribution networks on the FPGA in order to minimizes skew. There are only a limited number of these networks on ...

4

Cycle of clock means same as cycle for sine wave, i.e. from rising edge to next rising edge, or from falling edge to falling edge etc.

3

I suggest you look at using the PIC24F DMA controller to transfer SPI data directly into RAM. You'll have to read the datasheet to figure out what data rates are possible.

3

Most microcontrollers have a PMW/Counter logic block available that runs independently of the CPU. Check the datasheet to see if that's available on your micro, it's free and easy.

3

Asynchronous FIFO Asynchronous FIFO is an ideal approach to consider implementing between for crossing data safely across the two clock domains. If you are doing this in Vivado, I suggest you use the dedicated Vivado IP instead of designing one. If you are interested to design one, it would be useful to go thru this paper: Cummings's paper on FIFOs Choosing ...

3

Two key concepts: FPGAs in general (and Xilinx FPGAs in particular) have clock distribution networks that are designed to deliver clocks with low skew across the entire chip. A PLL (or DCM) can be used as a zero-delay clock buffer. Combining these concepts gets your clock across the chip with essentially zero delay. simulate this circuit – Schematic ...

3

The shape of the waveform won't affect the fundamental frequency of a signal. However an oscilloscope is usually not the correct instrument to accurately measure frequency. It may only have an accuracy of 1% or so. As @glen_geek points out in his answer some oscilloscopes do have counter/timers built into the instrument that can give high-accuracy (typically ...

3

Generally, using a ripple count is not a good idea if you care about skew and/or decoding the output. So let's say you fix that. There's still the issue of inter-output skew and multiple outputs changing state, which can lead to glitches. There's several ways to address that: use a registered output for the decoded signal. Look ahead 1 state, decode that, ...

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