fwd: RE: Voltage mode driver penalty

RMoore at corp.adaptec.com RMoore at corp.adaptec.com
Wed May 15 11:04:00 PDT 1996


* From the SCSI Reflector, posted by:
* RMoore at corp.adaptec.com
*
Form: Forward
Header: Adaptec Company Confidential
Text: (23 lines follow)
Gerry Houlder wrote:

> * From the SCSI Reflector, posted by:
> * Gerry Houlder <Gerry_Houlder at notes.seagate.com>
> *
> The different operating modes of current mode versus voltage mode drivers 
> appears to be significant. Does this mean that devices with "voltage mode" 

> drivers may not be able to coexist with devices that have "current mode" 
> drivers? If there is any chance of intermix problems, we had better 
specify 
> only one type.

No, its not a problem of interoperability since both voltage and current 
mode devices
will achieve good signal levels. My problem, if it is a problem, is that the 
compliance
test circuit doesn't allow as much design tolerance for voltage mode drivers 
as it could.
Thus, voltage mode devices have to be over-designed to comply with SPI-2.

	Richard Moore
	Adaptec Irvine Technology Center
Original text: (22 lines follow)
>From owner-scsi at Symbios.COM, on 5/15/96 1:43 PM:
To: scsi at Symbios.COM (scsi)

* From the SCSI Reflector, posted by:
* Gerry Houlder <Gerry_Houlder at notes.seagate.com>
*
The different operating modes of current mode versus voltage mode drivers 
appears to be significant. Does this mean that devices with "voltage mode" 
drivers may not be able to coexist with devices that have "current mode" 
drivers? If there is any chance of intermix problems, we had better specify 
only one type.

I recall that IPI had different (and somewhat incompatible) driver circuits 
for 
voltage mode and current mode. This was one of the things that made IPI 
unpopular because the customer always had to make sure that all devices used 

the same style of driver and each vendor only supported (or wanted to 
support) 
one style. I hope we don't end up with a similar situation for LVD SCSI.


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