On 10 Dec 98 at 2:45, Changhsu Liu wrote:

> I'm changing my internal Panasonic 7502b to an external one. One thing I
> cannot figure out is to set up jumper of SCSI ID so that the SCSI ID can be
> set from the switch outside the box.

  Oh boy.

> By reading the simple instruction comes with the external case, it seems
> that I should put:
> RED to pin1,
> BLUE to pin2,
> YELLOW to pin4, and
> BLACK to COM.
>
> From Panasonic jumper info:
> 1 to 3 for scsi ID control,
> pin4 : parity,
> pin5: no pin,
> pin6: terminator,
> pin7: term power.
>
> Result:
> Since I took pin 1 to 3 out and put the corresponding connectors in, my
> computer recognize it as SCSI "0" no matter what number on my switcher.
>
> Here are my questions:
> 1) I can find corresponding pins for red, blue, and yellow lines from the
> back of panasonic, but where do I put the BLACK one, Which pin is COM?

  The black line goes to the common supply or ground.  Basically, the
second pins of all three pairs need to connect to the black line, and
it matters which side of the pairs that is.
  [My suggestion:  Take an ohmeter (volt-ohm meter, set for ohms),
and apply it across the upper pins of the first two pairs.  If the
resistance drops to zero, the upper pins are connected in common, and
this is where the black line goes.  If not, try the lower pins --
it's pretty likely that one or the other will be connected this way.]
  In order to sense which pairs of pins are connected, the controller
needs to (effectively -- electrical details may be a little more
complicated) send out a signal on common (black) and see which pins
the signal comes back on.  If there's no circuit from common, through
the selector on the external case, to the other pin of each pair, all
settings will read "000", or zero, just as you've found.

> 2) Each jumper pin in the back of panasonic has 2 pins (top and bottom),
> but the lines for each pin ID from the external case has only one
> connector. Do I connect the top one or the bottom one? (I have tried on
> both but it didn't make any difference. The SCSI ID number cannot be
> controlled by ID switch.)

  I think this is probably answered above.

> 3) What are the functions of jumpers on pin 6 (terminator) and pin 7 (term
> power)? When pin6 is ON, does it mean it's internally terminated that I do
> not need a terminator if my drive is on the last of the scsi chain?

  You are correct.

> 4) From the back of the panasonic, I can see numbers 1, 2, 4 on the
> location of pin1, pin2, pin3. Why do they call pin3 "4"? The number does
> match the description in the instruction of the external case. There must
> be a reason for the number being "4" instead of "3", but why?

  These are powers of 2 -- we're counting in binary:

    4 2 1
0 = 0 0 0
1 = 0 0 1
2 = 0 1 0
3 = 0 1 1
4 = 1 0 0
5 = 1 0 1
6 = 1 1 0
7 = 1 1 1

So you can calculate the drive ID from which pins are jumpered.  [Or
conversely, figure out which pins to jumper for what ID....]

> 5) Is there a restriction on the scsi number you can use on PC? I know "7"
> is reserved for system for Mac. Is it the same with PC?

  7 is typically used for the SCSI controller.  Some PC OSes will
only boot from device 0; my practice has been to put hard drives on
0-3 and other devices (CD, CD-R, Zip, etc) on 4-6, but that's
voluntary.

David G

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