[comp.sys.mac.misc] Apple SCSI termination

rankins@argentina (raymond r rankins) (08/18/90)

Does anyone have a schematic or some sort of diagram or instructions for
building an Apple compatable SCSI Terminator?  This is for an Apple IIGS
with Apple's SCSI card.  I can't see paying $15 to $30 for something 
that probably costs about $5 in parts.

Anyone have any they want to sell cheap?

I am putting together a case with Quantum SCSI drive and a 3M tape drive
in it.  What is the best way to wire this up and terminate it?  Someone
recommended that the tape drive be at the end of the SCSI chain. Here is
what I've come up with so far:  ([] = 50 pin Centronics connector)

 SCSI in     SCSI out

   []           []     []    []                    []
    \           /       \____/\                     \
     \  _____  /               \  _____              \  _____
      \/     \/                 \/     \              \/     \
     _||_   _||_               _||_   _||_           _||_   _||_ 
    |    | |    |    OR...    |    | |    |   OR... |    | |    |
    |    | |    |             |    | |    |         |    | |    |
    |    | |    |             |    | |    |         |    | |    |
    |    | |    |             |    | |    |         |    | |    |
    |____| |____|             |____| |____|         |____| |____|
  
     Disk   Tape               Disk   Tape           Disk   Tape

       Fig. 1                     Fig. 2                Fig. 3


I believe someone posted in comp.periphs.scsi that Fig. 1 is the
proper way that a case should be wired.  If so, is it okay just to
install the resistor packs directly on the tape drive to terminate the
SCSI bus?  Would I need any further termination like on the SCSI out
connector in Fig. 1?

Fig. 2 doesn't seem at all right for a bus system like SCSI, but
that's the cable set up that came with the case.  Where would you
place the terminators in a set up like that?  Which connector should
be the SCSI in, or doesn't it matter?

If I don't care if the set up is daisy chainable, would Fig. 3 be my
best bet and just install the terminator blocks on the Tape drive?

Thanks in advance,
Ray

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