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termination
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1998-05-02
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112 lines
HOW TO CORRECTLY SET UP A SCSI TERMINATION
The termination must be connected on the first AND on the last
scsi device.
Term. UnTerm. Term.
Controller --------- [n] Device --------- Last Device
Example:
Term. UnTerm. Term.
Controller --------- Cd-Rom -------- HardDisk
Only one exception is allowed:
If you have an internal and an external scsi chain, you can leave the
internal chain unterminated if the chain is shorter than 10 cm.
Example:
Internal Chain External Chain
UnTerm. 8cm Term. UnTerm. Term.
HardDisk ------ Controller ----- Cd-Rom ------ HardDisk
Different combinations may work, but is better if your scsi chain
works following the scsi standard.
The need of an extra termination is a symptom of a bad scsi chain...
Better you substitute your old scsi devices with new ones.
SOME OTHER SCSI TECHNICAL RESTRICTIONS
The maximum length of a SCSI chain is 6 meters.
If you want to have a T ramification you should follow some rules:
min 30cm
|------------------------------|
Cable ----------T------------------------------T-------------....
| - |
| | |
| | 10 cm max |
| | |
| | |
| - |
Device Device
The minimum distance between two parts of the main cable is 1.27mm
(OkOk...it may also work if you leave only 1.26266267 mm :-) )
Example:
Cable -----------------+ min +---------- .....
| 1.27 |
| mm |
| |
+------+
The impendance of the cable must be between 90ohm AND 140ohm,
better if is 132ohm.
Don't connect cables with different impendances.
A little note: Controller isn't the right term,
better you use Host Adapter.
Alessandro Zummo
P.S. Sorry for my english....