Fine Timing programming 
Author Message
 Fine Timing programming

I am trying to find out what separation between two pulses causes a
circuit to fail. When I try to reduce the clock low time the time
defined seems only to change in integral units e.g. 100ns , 200ns etc. I
have adjusted the `timescale such that it should be able to be
programmed with a high resolution. What have I missed? TIA for your
help.

There is only one `timescale in the whole file.
`timescale 10ps / 10ps

The period is equivalent to 100ns.
`define PERIOD  10000.0

This variable defines part of the time the clock is low.
real hightime;

   initial
      begin

         hightime = 3.5;

         #`PERIOD       I_IN_CLOCK = 1'b1;
         #`PERIOD       I_IN_CLOCK = 1'b0;
         #(hightime*`PERIOD)    I_IN_CLOCK = 1'b0;
         #`PERIOD       I_IN_CLOCK = 1'b1;
         #`PERIOD       I_IN_CLOCK = 1'b0;
--
Andy Botterill



Sat, 24 Dec 2005 02:48:45 GMT  
 Fine Timing programming

Quote:

> When I try to reduce the clock low time the time
> defined seems only to change in integral units e.g. 100ns , 200ns etc. I
> have adjusted the `timescale such that it should be able to be
> programmed with a high resolution. What have I missed? TIA for your
> help.

It should work.  How are you observing what time the clock edges occur?
Perhaps you are using some mechanism like a waveform tool that has its
own separate precision and is not showing the actual simulated time to
full precision.  What simulator are you using?


Sat, 24 Dec 2005 06:06:18 GMT  
 Fine Timing programming


Quote:


>> When I try to reduce the clock low time the time
>> defined seems only to change in integral units e.g. 100ns , 200ns etc. I
>> have adjusted the `timescale such that it should be able to be
>> programmed with a high resolution. What have I missed? TIA for your
>> help.

>It should work.  How are you observing what time the clock edges occur?

I've looked at the waveforms in more detail. I was looking at the wrong
level and was seeing the clock aligned signals not the testbenches
stimulus.

Apologies for the wild goose chase.

Quote:
>Perhaps you are using some mechanism like a waveform tool that has its
>own separate precision and is not showing the actual simulated time to
>full precision.  What simulator are you using?

I don't think it was the waveform display software. Modelsim.
--
Andy Botterill


Sat, 24 Dec 2005 20:16:53 GMT  
 
 [ 3 post ] 

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