SPI-3 single-ended AC test circuit

Gene_Milligan at notes.seagate.com Gene_Milligan at notes.seagate.com
Wed Jun 30 06:24:49 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* Gene_Milligan at notes.seagate.com
*
The specification was originally formed based upon rise time and the value
picked as a tradeoff between crosstalk considerations versus available
setup and hold times. The original rise time values assumed relatively
constant slew rates but the committee thought this better translated into
slew rates. I think the spec assumed that the rates would apply to whatever
transfer rate was negotiated. However the slew rates are independent of the
negotiated offset and I think also apply even if the transfer reverts to
asynchronous in which case the frequency approaches zero (although not the
frequency components). While slew rates may be specified differently for
various negotiated synchronous transfer rates, some implementations may
find this to be problematic. Of course a regular (square wave) signal is
the preferred choice probably for measurement ease.

Gene

To:       Gene Milligan, John Lohmeyer <lohmeyer at ix.netcom.com>
cc:       T10 Reflector <t10 at aztec.co.lsil.com>, "Barnes, Larry"
          <Larry.Barnes at lsil.com>
From:     "Stefek, Steve" <Steve.Stefek at lsil.com> @ INTERNET
Date:     06/29/99 08:17:59 PM GMT
Subject:  RE: SPI-3 single-ended AC test circuit




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

-----Original Message-----
From: Gene_Milligan at notes.seagate.com
[mailto:Gene_Milligan at notes.seagate.com]
Sent: Friday, June 25, 1999 6:01 PM
To: John Lohmeyer
Cc: T10 Reflector; Barnes, Larry
Subject: Re: SPI-3 single-ended AC test circuit


* 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


*
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at symbios.com



*
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at symbios.com





More information about the T10 mailing list