Can the external IO port of the FPGA be used as the input of the external clock??? 10

Guess, the reason why you're outputting a two-way is this.

always@（negedge clk_in)out = ~out;

In this way, each falling edge of the clk in is out flip once, of course, it is a two-way frequency. I made this mistake when I was a beginner.

Also, it is very important to note that ordinary IO as a clock signal generally needs to be processed before it can be used as a clock, otherwise it will be too affected by the glitch, and if possible, a high-speed clock will be used to detect the edge of this signal.

I have also encountered such a problem before, it is very puzzling, it is best to connect the clock to the clock pins, or add a driver chip to shape the signal, which is caused by the signal clock is not very good (the edge is not very clear). Blocking assignment q<=clk It's useless to write like this! If you want to assign values like this, you can use the equal sign, or you can connect them directly with lines.

e.g. assign q=clk; And which FPGA chip do you use? Different chips have different driving capabilities.

Q<=clk, can't you write like that? Did you use a phase-locked loop? Is the input frequency right?

Theoretically, yes, but you need to pay attention to it when using it, too many clocks can cause interference between each other, and data disorder will occur if it is not handled well.

FPGA (Field Programmable Gate Array) is a product of further development on the basis of programmable devices such as PAL, GAL, and CPLD. It appears as a semi-customized circuit in the field of application-specific integrated circuits (ASIC), which not only solves the shortcomings of custom circuits, but also overcomes the shortcomings of the limited number of gates of the original programmable devices.

It is best to input the clock signal through a dedicated clock pin, otherwise it is prone to problems.

Put it on top of a dedicated clock interface. For the specific one, please check the datasheet of the corresponding chip

The CLK pin can be used as an ordinary input pin, when used as an input function, it is the same as the ordinary IO function, but the CLK pin cannot be used as an output function, if not in use, it can be suspended, and it does not need to be grounded, you just need to set the useless pin to a three-state input when building a project, which is the usual way to deal with it.

The dedicated clock (global clock) pin can be reused as an IO pin, but it is not recommended to use it if the pin is not sufficient.

No, the FPGA is a digital signal, the sensor output is an analog signal, and the AD needs to be connected in the middle

You need to confirm a few points:

Whether the sensor is a voltage output or a current output.

1 For voltage output, what is the maximum voltage, and it cannot exceed the IO voltage of the FPGA (most FPGA IO voltages are TTL), otherwise it is easy to damage the chip. Several resistors can be stringed to take the voltage divider value as the FPGA input. Although there will be a certain deviation, it depends on your needs.

It's still okay to just take a high and low level.

2 If the current output, you can connect a resistor, and pay attention to the voltage at both ends of the resistor should not exceed the IO voltage.

Don't forget that the sensor ground and the FPGA ground should be connected.

It depends on whether the output of your sensor is digital or not.

Use the input and output pins, but pay attention to the control method when using, and sensible electronic design VGZ

Yes, you can also connect any Io, if it is used as a global clock, it is best to connect to a dedicated clock input pin, in addition, if you use an internal PLL, it is best to connect a dedicated clock pin, the general clock pin can not do ordinary Io, can only be a clock input or ordinary input!

I don't understand what it means, what 400MHz clock input.

Is it LVDS that receives an external 400MHz clock signal?

One port transmits 8 data in one cycle, but it can't. Either 8 cycles, or 8 ports, and if you have a long cycle, you can increase the output frequency, which means that the cycle of your output is different from the cycle you require. It's awkward

What is a clock cycle? I think the 100MHz you are talking about is actually the output frequency of the crystal oscillator. As for whether the clock period is or not, of course, it should be set by you via PLL.

So you can do this by dividing and counting. Otherwise, 700MHz is really too high, the key is how do you detect the output.

You need to multiply txclk by 8 times, and then send one bit of data per cycle, so that you can do it. If it is parallel, that is to say, if it transmits 8 bits at a time, then there is no need to multiply, which is why the parallel speed is fast and the output speed of serial output is slow.

You can only operate on 8x clock