8 digit frequency counter


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I've just finished my 8 digit frequency counter - I'm just waiting for a GPS module to arrive so I can use it as the reference timesource.

Here's a block diagram of the project:


And here is a photo of it in action, when using a one pulse per second generated from the local Xtal as the reference.


Full source is up on my wiki at http://hamsterworks....equency_counter

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I've updated the project to now work at up to 100MHz by added a DDR Input to the edge detector.

Here is a video of it displaying what should be a 96.875 signal - the xtal is about 20ppm fast, when using the Papilio One as a reference. Only the last digit flicks up and down, until I touch the oscillator toward the end. Note the ghetto twisted pair required to get the test signal onto the Papilio One :-). The +- 20Hz dip at the end is when I put my finger on the Nexys2's oscillator!

And just to prove my loathing the the Basys2's oscillator is well founded, here is a video comparing the stability of the Nexys2 and Basys2 boards:

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  • 2 months later...

Hello all,


maybe I have a stupid question but I'm unsure how to connect the Display unit from Dealextreme to the papilio. As far as I found this Display likes a Vcc of 5V. This 5V obviously is supplied through the Papilio. The IO of the Xilinx isn't 5V tolerant isn't it? Can someone explain me, why it is possible to connect the papilio and the display anyways please? 


Should I study the datasheet more in depth?




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Thanks Mike for clearing things up


I was confused because of Page 4 pin function in the data sheet  Vdd is stated to be 5V +/-10% 

On page 12 electrical characteristics Vdd is called logic supply voltage in the range -0.5 to 7V


Now I understand the tables on page 12 a way better. 5V for Vdd is recommended but not a demand. For a logical high 0.7Vdd is the minimum value (2.31V with 3.3Vdd) and low should be beyond 0.99V


Again thanks a lot


Many regards 


Hi Peter


The display also works at 3.3V.



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