How to change clock frequency of Xilinx XSA 3S1000 Board?

Hi everybody,

I'm an Electrical and Electronics Engineering student. For my term project I need to implement an FPGA design which uses VGA interface. Xilinx XSA 3S1000 board has a 100 MHz fixed clock frequency and I need to change that to 25 MHz.

Our instructors and FPGA board datasheet are not helpful. Datasheet say that I need to program CPLD on the board so that it can divide clock frequency. But I have a very limited knowledge on FPGA boards and don't know how to do that. I'm searching the web with my friend and got nothing so far.

Any help appreciated. Thanks.

Hi,

You can just use a DCM to divide your 100Mhz by 4 to get the 25Mhz clock.

thank you.

As the board is equipped with 100 MHz oscillator and VGA output, I'm rather sure that you'll find VGA demonstration projects working with 100 MHz input clock.

What are you trying to achieve? Copy an existing VGA video design with 25 MHz clock or writing a VGA interface from the scratch? In both cases it seems appropriate to spend an hour or two learning about FPGA clocking options.

We don't know anything about FPGA boards. In our labs we use manuals prepared by lab instructors and in these manuals they say what we need to to step by step: click there, then click there and do this and you are done. We actually don't learn how to use them but they want us to use these FPGA boards and VGA to do our term project. Also we didn't learn anything about VGA. It may be easy to search and learn them if you know the basics but it is a huge step to learn the basics. If I had a basic knowledge about how to use these things I would be able to search the internet and find the answers. But we don't know even where to start. So, a little more help would be great.

How to do it by using DCM? And what is DCM?

Our instructors want us two change clock frequency to 25 MHz. Also we have no experience on the subject. We need to benefit from the examples on the internet.

Thanks.

zarax said:

We don't know anything about FPGA boards. In our labs we use manuals prepared by lab instructors and in these manuals they say what we need to to step by step: click there, then click there and do this and you are done. We actually don't learn how to use them but they want us to use these FPGA boards and VGA to do our term project.
Thanks.

Click to expand...

Yikes, I hope this university is free, because that is just plain useless for learning anything (you get what you pay for). Any job you get out of school isn't going to have a manual to tell you step by step how to do a job.

zarax said:

Also we didn't learn anything about VGA. It may be easy to search and learn them if you know the basics but it is a huge step to learn the basics. If I had a basic knowledge about how to use these things I would be able to search the internet and find the answers. But we don't know even where to start. So, a little more help would be great.

Click to expand...

Just search for "VGA Timing" "vga protocol" or something similar to find out what the VGA signals look like. I've never worked with VGA, but the timing interface looks pretty simple. It appears you'll just need a bunch of counters to keep track of time and toggle signals at the appropriate spots.

zarax said:

How to do it by using DCM? And what is DCM?
Our instructors want us two change clock frequency to 25 MHz. Also we have no experience on the subject. We need to benefit from the examples on the internet.

Click to expand...

A DCM is a Digital Clock Manager, You should really read the Xilinx documentation for the FPGA on that board. FYI, when you graduate, this is what will be expected of you by your employer to learn what you need to know to use new parts and get your job done. And to use the DCM you create a new core using Xilinx's core generator. The wizard will give you options to select the input frequency and the output frequency of the DCM. This is also in a document that can be found on Xilinx's web site.


Regards

Thanks ads-ee.