scsi allmänt

Förrutom att varje SCSI-enhet inklusive kortet måste ha ett unikt ID,måste man oftast också ha en terminator som avslutar kedjan.
Sen kräver en del SCSI-kort att man måste Initiera,formatera och partionera disken i SCSI-bios.
Dessutom måste man ibland också ladda drivarna till kortet när man installerar Windows.

Tyvärr kan det skillja sig väldiga mellan olika SCSI-kort,en del har själv-terminering,en del finns det drivare i Windows till osv...
Det bästa är att läsa på om SCSI i allmänhet och om ditt kort och diskar i synnerlighet.
Det är inte säkert att vad som gäller för en setup,funkar med en annan...

TERMINATION - basics

Why terminate?

A pulse propagating along the SCSI bus will ‘reflect’ from any rt of the bus that is different from the rest of it. These reflections add and subtract in odd combinations and cause the original pulse to be distorted and corrupted, thereby causing data loss. To prevent or minimize reflections from the ends of the bus, terminators are added to "absorb" the energy from the pulses.

The terminators on the SCSI bus hold the bus in a negated state, any one of up to 16 drivers could be driving the bus or none. The bus is held in the negated state as required by the SCSI protocol. The original drivers on a SCSI bus only asserted (Open collector) and the terminators were used to negate the bus. Drivers that assert and negate the bus are known as active negation drivers. The negation is less current than the assertion, the drivers are designed for 2 terminators negating the bus.

Where do you terminate the bus?

[Terminate: from the latin terminus meaning "the end".]

Termination must be present at two and only two positions on the SCSI bus, at the beginning of the bus, and at the end, and must occur within 4 inches of the physical ends of the SCSI bus. Often, the host will be installed at one end of the bus, and will provide one of the two terminations required.

When do you terminate the bus?

Always. Period. Whenever you want the SCSI bus to operate reliably!

How are terminators powered?

Terminators are powered from the "term power" line on the SCSI bus. Term power can come from any device on the bus, and is provided by either the host, a drive on the bus, the backplane, or any combination thereof. Term power is provide through a diode and fuse - historically - the drop accross the diode and cable allows for a term power range of 4.0 to 5.25 volts.

What kinds of terminators are available?

Internal: some SCSI drives (pre-LVD) had passive terminators installed in the drive, and could
be enabled/disabled by setting a jumper or inserted/removed from a socket. Drives with
LVD interface do not have internal termination due to reduce bus loading, and the fact that in a multi-drive
environment, only one drive needs to be terminated.

External:

In-line (also called ‘feed-through’) terminators connect in series with a SCSI device.
Close-ended terminators plug into a bus connector or may be crimped on the cable.

Passive: resistor networks driven directly by the term power on the bus.
Active: resistor networks driven by voltage regulators inside the terminator. All LVD
terminators can be assumed to be ‘active’.

What is the difference between passive and active termination?

Passive termination is a resistor network, 330 ohms from ground to the signal line and 220 ohms from the signal line to termpower, which is an equivalent impedance of around 132 ohms. Since typical characteristic impedance of most cable is between 85 and 110 ohms, this is not a great match. The negation current varies with the term power voltage which can be from 4.0 to 5.25 volts, the pull up current would range from 16.5 to 24 mA. This would often required multiple steps to insure the voltage reached the 2.0 volt at the receiver. An active termination incorporates a small voltage regulator which generates a stable termination voltage from the raw Term Power (which may fluctuate) and allows the termination resistance to be lowered to 110 ohms, more closely matching the cable impedance. Active termination is recommended for all Single Ended buses at any speed, and is required for Single Ended Ultra SCSI speeds and above. New systems with active terminates may be powered from a 3.3 volt source, termpower can be from 2.7 to 5.25 volts.

(Tack Jenza för länken.)

*Edit:En till bra länk om SCSI
http://www.paralan.com/artech1.html

*Tittar på mitt U2W-kort som är till salu.....*

behövde inte jumpra något på min scsi disk. Köpte adaptec 19160 kort retail med kabel å terminator sedan vart det bara å koppla disken på sissta kontackten innan terminatorn enligt manualen å det fugnerade fint.