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Simulators >> Circuit Simulators >> Can I group a bus?
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Message started by ywguo on Apr 9^th, 2007, 12:24am

Title: Can I group a bus?
Post by ywguo on Apr 9^th, 2007, 12:24am

Hi, Guys,

I simulate a thermometer encoder using Spectre in analog design environment. The graph tool is wavescan. For. eg., the encoder has 64 output, can I group the bus and display it in binary mode?

Thanks
Yawei

Title: Re: Can I group a bus?
Post by Andrew Beckett on Apr 11^th, 2007, 7:31am

Assuming you have a bunch of voltage waveforms, one for each bit, then this is what you do:

1. Plot all the voltage waveforms, and then select them all.
2. Select the a2dDialog icon
3. On the form that pops up, you can then enter the thresholds for converting these to digital signals (either a single threshold or a high/low threshold). You can choose where to plot the new signals.
4. Having got your new digital signals, you can select them and convert them to a bus. You may want to drag them around first so they're in the right order, or use ctrl-select to select them one at a time in the right order. Then use the Create Bus Icon.
5. A form will appear (you'll probably want to expand it, and drag the signal column to be wider, so you can see which bit is which) and click on the Bit column if the bus is in the wrong order. Choose the radix you want, and where to plot it, and hit OK.
6. You can then do fun things like select the resulting bus, and convert it back to Analog (using Busses output as Analog Voltage) so you can see an analog representation of the bus waveform.

Regards,

Andrew.

Title: Re: Can I group a bus?
Post by Ken Kundert on Apr 11^th, 2007, 8:03am

Andrew,
How is the waveform tool interpreting the data on the bus? Is it really capable of properly decoding a thermometer code?

-Ken

Title: Re: Can I group a bus?
Post by Andrew Beckett on Apr 11^th, 2007, 8:07am

Ken,

Well, if converting a set of bits into a bus, then this is just representing it as a simple bus - not doing any encoding. I was assuming that was what was wanted here.

That probably doesn't matter, unless you're trying to then represent that bus as an analog waveform (step 6 in my previous post) - for thermometer coding that wouldn't be terribly useful.

Regards,

Andrew.

Title: Re: Can I group a bus?
Post by Ken Kundert on Apr 11^th, 2007, 10:25am

Andrew,
You might want to pass on to the display tool development team that different types of decoding would be very useful. In my experience, analog designers often use binary, two-complement, gray, and thermometer codes.

-Ken

Title: Re: Can I group a bus?
Post by ywguo on Apr 12^th, 2007, 11:37pm

Hi, Andrew,

Thank you. I did it as what you said. It's easy to use.

Yawei