Load Capacitance

Gene_Milligan at notes.seagate.com Gene_Milligan at notes.seagate.com
Wed Oct 14 08:58:22 PDT 1998


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Gene_Milligan at notes.seagate.com
*
Since the tight tolerances are in LVD mode, the LVD measurement
requirements of 7.2.4 of SPI-2 should be used. If you follow those
requirements I think you will conclude that the drive has to either be in a
power off condition or if not in a bus free condition. Obviously the
enabled terminator would require bus free with power on. The reason for
this conclusion is that is the only way to get both the plus and minus
signals at the same voltage level without loading special firmware to
interact with the capacitance measurement.

If the device passes the LVD test it will obviously pass the single ended
test since the single ended requirements are looser. Annex H for the single
ended measurement specifically states that power is removed and the common
lines are connected together. Although it does not require that all common
lines are connected together the real common grounds should be included
since (as I assume your question was directed at) the individual common
line for the specific signal in a multimode drive is not connected to
ground but to a unpowered driver which if it were powered and driving the
ground return line would be providing low impedance path to the common
ground.

Gene

To:       "'T10 at symbios.com'" <T10 at Symbios.COM>
cc:        (bcc: Gene Milligan)
From:     "McSorley, Greg" <gmcsorley at clariion.com> @ INTERNET
Date:     10/14/98 03:01:50 PM GMT
Subject:  Load Capacitance




* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* "McSorley, Greg" <gmcsorley at clariion.com>
*
Good Morning
If I want to check the load capacitance of a disk drive with a muti-mode,
SE--LVD, SCSI devise, do I measure it S/E or differentialy. If I measure
S/E, can the usual RTN line for the signal be used as ground for the
measurement?
Thanks
*
* 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