extending a signal pulse

Jul 08, 2004 3 Replies
J

Hi all,



What would be the optimal way, in terms of device utilization and=20 functionality, to exstend the length of the time a signal is asserted=20 from one clock cycle to four clock cycles. I.e. [pseduo code:] if signal_a is asserted then signal_b is asserted for four clk;



Is it possible to accomplish the function by utilizing an SRL16, or is=20 there a better solution? Or should I simply create four delayed versions =



of signal_a, and OR them together to form signal_b?



I'm working with a Virtex-2 device.



regards



--=20



----------------------------------------------- Please remove the x's in the email address if replying to me personally.



Johan Bernsp=E5ng, snipped-for-privacy@xfoix.se


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A

There is no precise answer U can give without knowing all the aspects of your problem.

For instance, your proposal to have an OR function may be dangerous if you use the result directly or indirectly as a clock to some other logic. In that case, I am pretty sure the output will glitch, which is not a problem at all if the output signal is reclocked for further use.

Apart from that remark, many solutions are possible, as you stated. Just try them . Another idea is to use a two bit state machine that controls an output flip-flop.

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R

I have used a 3-bit synchronous loadable counter for this task. MSB is high for 4 ticks, and serves both as count-enable and output. You can count either up or down.

This uses 3 registers. With 2 registers you could count 0,1,2,3,0=stop, output would be OR of both registers and the input.

Now an SRL16 can be 16 registers, so as you say perhaps there is a clever solution with this...

-rajeev-

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G

You could use a SRL16/DFF (with clock-enable and synchronous clear) combination for this. The input pulse - which is high for one clock cycle -sets the FF output, and a delayed version of this pulse clears it after a number of clock cycles. The depth of the SLR16 sets the length of the output pulse. Note that the output pulse is delayed by one clock cycle with respect to the input pulse. _______ | |

+--| SRL16 |------+ | |_______| | | | | ______ | | | | | short pulse -----+--|CE Q|----------- long pulse | | | 1--|D | | | | | CLK--|> | | | | | +--|CLR | | | |______| | | | +-----------------+

Regards, Guy.

Johan Bernsp=E5ng wrote:

is

versions

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