[Fwd: Re: SPI-2 driver waveform]

Alan Littlewood alanl at lsil.com
Thu May 15 13:23:52 PDT 1997


* From the SCSI Reflector (scsi at symbios.com), posted by:
* Alan Littlewood <alanl at lsil.com>
*
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Wally,  thanks for the response.  I am certainly in favor of saving a
tree,  BUT,  I'm still convinced that the drawing I have is wrong.  It's
difficult describe this without us looking at the drawing together, but
here goes.

The rise and fall times are shown as tr and tf, with black blobs drawn
on the waveform.  On the right hand side of the drawing,  the 0.8 Vss
shows the arrowhead at the positive level correctly, where the threshold
level is. (4th horizontal dotted line from the top).  
However the bottom arrowhead for 0.8 Vss is pointing to the stabilized
negative dc level (2nd horizontal dotted line from the bottom) instead
of the negative threshold point (4th horizontal dotted line from the
bottom.

Then look closely at the three references to the 0.2Vss at the negative
level for overshoot.  There is one too many. Specifically, the one to
the farthest right.  It is drawn between the threshold level and the
stabilized level.
 
This is what my drawing looks like and it doesn't make sense.

Regards,

Alan.

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Date: Thu, 15 May 97 11:29:57 PDT
From: wally at eng.adaptec.com (Walter Bridgewater x2371)
Message-Id: <9705151829.AA03673 at eng.adaptec.com>
To: scsi at Symbios.COM, alanl at lsil.com
Subject: Re: SPI-2 driver waveform
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Alan,

I believe the figure is correct.  Figure 33 is used to show to
different things:

1) show the over/under shoot levels
2) show where the 20% & 80% points are for rise/fall times 

If you try to interpet the figure as only showing overshoot, I agree
you will be confused, but, save a tree.


Wally

> From scsi-owner at Symbios.COM Wed May 14 10:30:10 1997
> Return-Path: <scsi-owner at Symbios.COM>
> Date: Wed, 14 May 1997 10:04:37 -0700
> From: Alan Littlewood <alanl at lsil.com>
> Organization: LSI Logic
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> To: scsi at Symbios.COM
> Subject: SPI-2 driver waveform
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> 
> * From the SCSI Reflector (scsi at symbios.com), posted by:
> * Alan Littlewood <alanl at lsil.com>
> *
> In the X3T10/1142D Rev.11 document I think there is an error in the
> waveform drawing on page 50.  Figure 33.
> 
> At the negative voltage level, there are three references to 0.2Vss for
> overshoot spikes.  It seems to me that there should be only two
> references, the same as shown at the positive voltage level.
> 
> Secondly, the reference arrowhead for 0.8Vss is shown at the wrong point
> at the negative level.
> 
> If I am wrong and the drawing as shown is correct, can someone explain
> why it has to be this way.
> 
> Thanks,
> 
> Alan.
> *
> * For SCSI Reflector information, send a message with
> * 'info scsi' (no quotes) in the message body to majordomo at symbios.com
> 




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