osillator

[elnaz]

Hello
I need a vhdl code for an (500k-1M) oscillator,could anyone please help me?!!

 

[bmcculla]

Are you using the oscillator for simulation? As far as I know you can't implement a oscillator in a CPLD or FPGA. I have seen people build a crystal driver to generate a clock signal but you need external components.

If you give more information about what you are trying to do we might be able to help you more.

 

[elnaz]

yes,I am trying to implement a circuit including a built in oscillator on a fpga using xilinx foundation 4 software.
but the problem is the virtex family(my circuit works only on this family) library dosen't have osc4 which spartan family dose, and so on it can not be implemented,thus I am trying to find a vhdl code.

 

[bmcculla]

The osc4 you are talking about seems to just drive a relaxation oscillator. A relaxation oscillator is just a NOT gate and a RC circuit. For 500k-1MHz you are probably better off going with a crystal. A simple parallel crystal oscillator should be easy to build. You need the external components - an oscillator can't be generated with only VHDL.

 

[Optikon]

yes,I am trying to implement a circuit including a built in oscillator on a fpga using xilinx foundation 4 software.
but the problem is the virtex family(my circuit works only on this family) library dosen't have osc4 which spartan family dose, and so on it can not be implemented,thus I am trying to find a vhdl code.

You cant synthesize a VHDL oscillator without existing hardware that supports it! Spartan family was the last time they included a built in hardware osc (which is why you can instantiate one in that part)

You can write VHDL that does a simple bit toggle for simulation of a clock signal. But it is for simulation only and will not synthesize an oscillator.
The fpga is a _digital_ part and does not contain R&C's that would be necessary for an oscillator. The spartan had a very crude one but like I said, that was the last time. Which by the way that oscillator is NOT suitable for use as a clock. Use it only for blinking LEDs or for some inaccurate time measurements (cuz thats what you'll get!).

You need to bring in an external clock source.