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[/] [socgen/] [trunk/] [doc/] [src/] [guides/] [reset_sys_design.html] - Diff between revs 27 and 28
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<li>pll lock time</li>
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<li>pll lock time</li>
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</ul>
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</ul>
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You are looking at activity that is measured in the milliseconds on a
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You are looking at activity that is measured in the milliseconds on a
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system clock that is measured in the nanoseconds. Performing a reset in
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system clock that is measured in the nanoseconds. Performing a reset in
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one clock cycle requires adding logic to every single flipflop<br>
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one clock cycle requires adding logic to every single flipflop<br>
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for no good reason. A designer should only add reset logic as a last
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to provide nanosecond resolution to an event that is measured in
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microseconds. A designer should only add reset logic as a last
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resort. The preferred method is to use the existing mission mode logic
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resort. The preferred method is to use the existing mission mode logic
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to perform the reset. If you have a computational block with a fifty
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to perform the reset. If you have a computational block with a fifty
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stage deep pipeline then reset should force it's inputs to 0 and open
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stage deep pipeline then reset should force it's inputs to 0 and open
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all the gates so that every flipflop will be flushed out in 50 clocks.
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all the gates so that every flipflop will be flushed out in 50 clocks.
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Better yet would be to have the block feeding your input force it's
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Better yet would be to have the block feeding your input force it's
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</p>
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</p>
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<p><br>
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<p><br>
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<br>
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<br>
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</p>
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</p>
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<p><br>
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<p><br>
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<br>
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</p>
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<h3 class="western">8) Seperate Synchronous and Asynchronous
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resets<br>
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</h3>
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Asynchronous
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resets connect to the asynchronouse reset/preset ports of a flip/flop.
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Synchronous resets connect through the logic cone to the D flip/flop
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port. They are the logicaly the same signal in mission mode but must be
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sperate during scan testing. It is very easy to make a mistake in
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rtl coding. The recomendation is the use active low signals for
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all asynchronous resets and active high signals for all synchronous
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ones.<br>
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<p><br>
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</p>
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</p>
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<p><br>
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<p><br>
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<br>
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<br>
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</p>
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</p>
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<p><br>
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<p><br>
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