Re: PCC error
Gene Heskett sends Greetings to Richard Hirst;
>On Fri, Sep 07, 2001 at 10:51:11AM -0700, Rick Eicher II wrote:
>> I have to to enter them but it tells me what the defaults are.
>OK, different from my manual.
>> This pcb is about two inches wide and four inches long? If so the fuse is
>> green? It is bad. It will not pass current.
>That's the pcb, don't know what colour your fuse might be - sorry, I don't
>have oneI can look at right now.
>> This would cause the pcc command to throw out the " scsi port reset signal
>> is active" error?
>Unpowered terminators might well pull the scsi bus reset line down which
>might result in that msg.
>Richard
No 'might well' about it fellows. It will. Please bear in mind that
the scsi bus, except for the lvd models, is a powered bus in that all
active devices are in fact open collector drivers and can only be turned
off which allows the terminators to pull it up to a logic 1. In other
words capable of pulling a conductor down to a logic zero against the
efforts of the terminators to maintain the nominally 3.0 volts of a
logic one, but incapable of independantly sending a logic 1, defined as
a voltage at or above 2.4 volts.
Without terminator power, the whole bus will be sitting within a few
millivolts of zero volts, a logic zero, hence the message.
Also, without term power, the input devices of any attached hardware
will also be unpowered as that is also part of the scsi rulebook.
So, even if the device on the end of the chain is actually set to supply
its own term power, but is prevented from sending that term power down
the cable, a common protective measure, then other devices in the middle
of the cable will have no input power, and will load the bus, at best
giving the bus erratic behaviour.
The scsi specification recommends that the host controller should
supply ALL term power for all devices on the cable as a method by which
offline devices that are only used occasionally but are left hanging on
the buss when turned off, will have power for their own inputs and will
not then load the bus to the point of making it mis-behave.
Cheers, Gene
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Gene Heskett, CET, UHK |Amiga A2k Zeus040, 70MB ram, 31 gigs
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This messages reply content, but not any previously quoted material,
is © 2001 by Gene Heskett, all rights reserved.
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