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Discussion Groups | FPGA-CPU | Re: Re: why FPGA?
This list is for discussion of the design and implementation of field-programmable gate array based processors and integrated systems. It is also for discussion and community support of the XSOC Project (see http://www.fpgacpu.org/xsoc).
Re: Re: why FPGA? - Jeff Brower - Jan 10 16:36:00 2005
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Rick- > It is not an issue of needing 5 volts out, the problem is that most > bus interfaces need bidirectional signals. It is not practical to use > a resistor to protect a pin when it also has to drive the signal. > Even if it is an output only, such as interrupt pins, if the signal is > pulled up to 5 volts, you have a problem. It protects it both ways. It works fine, everywhere we've tried it. -Jeff |
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Re: why FPGA? - Author Unknown - Jan 10 20:34:00 2005
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--- In , Jeff Brower <jbrower@s...> wrote: > Rick- > > > It is not an issue of needing 5 volts out, the problem is that most > > bus interfaces need bidirectional signals. It is not practical to use > > a resistor to protect a pin when it also has to drive the signal. > > Even if it is an output only, such as interrupt pins, if the signal is > > pulled up to 5 volts, you have a problem. > > It protects it both ways. It works fine, everywhere we've tried it. What? You can drive a shared bus using a 220 ohm series resistor? That would give you horrible rise/fall times. I guess if you are clocking a one-wire interface that would not be an issue. But any normal high speed bus will likely not work with that sort of a driver impedance. Or am I missing something here? |
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Re: Re: why FPGA? - Kolja Sulimma - Jan 11 3:14:00 2005
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wrote: >>ays. It works fine, everywhere we've tried it. >> >> > >What? You can drive a shared bus using a 220 ohm series resistor? >That would give you horrible rise/fall times. I guess if you are >clocking a one-wire interface that would not be an issue. But any >normal high speed bus will likely not work with that sort of a driver >impedance. > >Or am I missing something here? I just build a rather thin multi layer PCB. The impedance of a minimum width stripline of that board was 170R. An output with a 170R Resistor will give you the fastest possible settling time for that kind of wire. A lot faster than without the resistor. Kolja Sulimma |
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