SPI-3 single-ended AC test circuit

Walter Bridgewater wally at eng.adaptec.com
Tue Jun 29 14:22:09 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* wally at eng.adaptec.com (Walter Bridgewater)
*
Steve,

I think the calculation for 520mV/ns has been presented on the reflector
in the past.  It seems like somebody from IBM proposed the calculation
method.

But, basicly, 520mV/ns is a more exact statement of the how the slew 
rate was stated in the SCSI-2 spec.  It doesn't change it, just makes 
it more understandable.

Regards,

Wally


> *
> I notice that the SPI-2 Load circuit does not specify what frequency the
> driver should be running at when the slew measurement is made.  On cables,
> the slew rates will change depending on the frequency of the driving signal.
> Was there an "intended" frequency to be used for single ended slew rate
> measurements, or are slews relatively frequency independent on the SPI-2
> load because it is not a transmission line.  
> 
> Also, can anyone remember why the specified rate is 520mv/ns?  Have data
> failures been seen at a slew rate anywhere near this number?
> 
> Thanks,
> Steve
> 
> * From the T10 Reflector (t10 at symbios.com), posted by:
> * Gene_Milligan at notes.seagate.com
> *
> I recall that Kevin tried years ago to get the 15 pF raised to, I think,
> >100 pF and it took vigilance to avoid this change. The argument for the
> change was that the cable loading was much higher than 15 pF. The argument
> against the change was that the 15 pF was the gold standard the slew rates
> had been specd during the design phase.
> 
> Gene
> 
*
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