3 1/2" on the 7300

[D'Anne Thompson]

>From article <9595 at g.ms.uky.edu>, by david at ms.uky.edu (David Herron -- One of the vertebrae):
> In article <213 at toylnd.UUCP> dca at toylnd.UUCP (David C. Albrecht) writes:
>>Just thought maybe some other people might be
>>interested in this feasibility study.  Now I'm going to have to figure
>>out how to hook it up so I can switch between the 5 1/4 and the 3 1/2
>>(visions of 36 pin centronics switch boxes dancing in my head).  Getting the
>>distribution disks on 31/2s could be challenging.  Ah well, future food for
>>thought.
> 
> I've got something a little different planned.  I have a case & power
> supply for 2 half-height disks.  I also have a 3.5" disk kit from 
> tigertronics for making it look like a 5 1/4" drive.  I'm planning
> on putting both drives into that case, run a cable from inside the
> machine to the drives, and put in a toggle switch of some sort for the
> power only.  When I need to use the 5 1/4 I power it up, otherwise
> I power the 3 1/2.
> 
> How does that sound?
> 

Well,  Why not try this ?

Parallel cable from the Unix-PC to all drives.

Between the Unix-PC and the first disk, cut the 4 drive select lines
(DS0, DS1, DS2, and DS3) and install a two-way, three-way, or four-way
switch to route DS0 (coming from the Unix-PC) to DS0, DS1, DS2, and DS3
going towards the disk drives.  Install pull-ups (pull-downs) so the unconnected
DSx lines are not unterminated (May not be necessary. Would have to check).  

I would be concerned about having an unpowered disk drive on the bus
cable while another drive was running.

The Motor logic line (xx?) would turn on/off the selected drive motor
as necessary, but both drive interface boards would be powered up.

How does that sound ?

D'Anne Thompson
dat at noao.arizona.edu   	National Optical Astronomy Observatories.
			Tucson, Arizona