Date : Sat, 13 Apr 1991 11:54:00 CST
From : LANCE TAGLIAPIETRA <TAGLANCE@ucs.UWPLATT.EDU>
Subject: adding 3.5 inch drives
[NOTE: The following was originally posted on the BitNet list COCO@PUCC -
Tandy Color Computer discussion. Given the recent discussion on floppy
disk systems, this might be usefull to others on this discussion -- Lance]
Adding 3.5 inch Drives
These drive, as sold by most vendors, use 80 tracks, double-sided, and store
720 Kbytes of data. They are electrically the same as a 5 1/4 inch floppy
drives and can easily be added using the 80 track drives that have been
included with OS9 Level II. Also, several companies are selling adapter kits
to allow you to install these in a 5 1/4 inch drive enclosure. This is the
best way to go, but -- like me, many users will prefer to install them as an
addition to their current system instead of a replacement.
DRIVERS
As I said above, any of the drivers that are included with Level II can be
used as long as the 80 track descriptors are included in your bootfile for
the new disk drive. Microware has thougtfully provided descriptors for drives
/dd, /d0, /d1, and /d2 in 80 track double-sided format. All you need to do
here is make a new bootfile with the proper descriptors installed.
HARDWARE
The 3.5 inch drives use a different cable connector than the 5 1/4 inch units.
These are a 34 pin dual-header type connector with the same pin-out as the 34
pin edge card type. HOWEVER, these drives are also capable of receiving their
DC power through the ribbon cable, which is how Tandy powers them in their
new computer line. There is also a 4 pin power connector that my be used
instead. But, DO NOT provide power using the 4 pin power plug without
removing some of the pins from the 34 pin header type ribbon connector. If
you do, you will be grounding the power supply through the disk controller
card which will result in some major damage to the power supply, the
controller card, or both. If you use the 4 pin power connector, you must pull
all the ODD number pins from the connector, i.e., pins 1,3,5,7....etc.
None of these lines are used for any disk control signals so don7t worry
about that.
Addendum: Not all 3.5 inch drive manufacturers provide power to the
34 pin connector. On those drives that don't, there is no need to remove
any pins. However, if you are not sure, remove them anyway to protect
your power supply in case you are wrong.
The 4 pin power connector is wired in the same was as the older drive
connectors, with 12VDC on one end pin, 2 middle pins for ground, and 5VDC on
the other outer pin. You should ake sure which outer pin is for 12V and which
is for 5V before providing power to them or damage will result. My drive was
marked for the proper pins, but some may not be.
INSTALLATION
Being a practical minded (i.e. CHEAP) person, I installed my drive in a small
experimentors box, and tapped the power and the 34 pin connector off my
current dual disk drive package. Unless your current drives over-tax the
unit's power supply, this should be safe as they use so little power
themselves. So far, I have not noticed any power problems nor any increase in
the heat output of the power supplies voltage regulators. I haven't yet
measured the current draw, but I expect it to be very small. The 34 pin
ribbon cable connector was easy to find at the local Radio Shack store, but
the 4 pin power connector was not. So, I took another header connector and
cut it down to only 4 pins and used that for now. Later, I suppose I'll get
the "proper" one, but it's been working fine.
You should buy a new 34 pins ribbon cable and three 34 pin edge card
connectors that are designed to clamp on the cable. Measure at what points
you need to add the one or two connectors for your current drives, and then
add whatever lenght is required to extend the cable to the location of the
3.5 inch drive. Then, simply clamp the connector on.
I installed the drive on my system as drive /DD and am surprised that is it
noticably faster than my older drives. I then set the step rate to 6 ms using
DMODE, saved the changed descriptor back to disk, and COBBLER'd a new boot.
At
this step rate, all they do is "buzz" a little when accessing.
Eventually, I'll get another and have 1.4 meg of storage in these two tiny
units. The disks themselves are much easier to use, you need not be as
careful with them as floppies, and the are just neater! I feel like I just
discovered disk drives for the first time again.
Hope this helps some.
/\/\ark
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