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1994-07-14
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Msg #100 / 1-100 Time: 09 Jul 94 09:51:00
From: Wes Newell
To : James Micallef
Subj: Citizen Osda-39c 3.5 Driv
---------[A.ATARI.TECH]-----------------------------------------------
⇧MSGID: 51:202/0.0 2e1eb954
⇧REPLY: 51:5/10@ATARINET.FTN a8bf2702
Adding a 1.44 meg floppy to ORIGINAL ST's (NOT E's)
Things you will need:
1 HD disk drive. Preferably that supports output of density select.
1 Floppy controller chip capable of running 16 mhz (AJAX chip).
A TOS that will support HD drives. I use 2.06 with TAB board.
A format utility.
First let me explain the differences between the Atari (Epson SMD-340)
and some other drives. The Epson SMD-340 that Atari is currently selling
with the upgrade kit for the MEGA STE, DOES NOT have the capability to
provide an output of density on pin 2. This means that if you use this drive
you will have to use a switch to switch densities. As it comes from Atari,
it is jumpered as follows:
Pin 14-15 = Drive Select 0 (drive A)
Pin 5-13 = The mode (density) is switched by the HDI input (pin 2)
Pin 1-2 = The 2 meg mode (1.44) is set by the HDI input HIGH
Other jumper settings: 15-16=DS1, 6-7=DS2, 7-8=DS3, 2-3=2 meg mode set by
HDI input LOW, and 4-5=The mode is switched by the internal sensor.
As you may have figured out by now there are a couple of ways to hook
up this drive. On mine, I removed the 5-13 jumper and installed 4-5. This
lets the drive switch modes to 1.44 when a disk with the 1.44 meg extra hole
is inserted. The reason I did it this way is so I can easily tell my 1.44
disk from my 720K disk. If you want to use disk without the extra hole for
both densities, then leave 5-13 jumpered and configure jumper pins 1-2 or
2-3 depending on how you want to control the density, with a high (+5) or
low (ground). You must then manually switch the density.
Now you must also be able to switch the 8 mhz clock going to pin 18 of
the floppy controller chip to 16 mhz for HD (1.44) operation. I simply bent
the pin out and connected it to the center post of a spdt toggle switch and
connected the 8 mhz clock (from the empty pin 18 socket) to one side, and
connected the other side to 16 mhz (pin 39 of video shifter chip). You could
also have a switch to control an IC that would allow you to control both
clock rate and density select with one switch, or use a dpdt switch.
Drives that CAN output density select on pin 2.
Using a drive that can OUTPUT density select on pin 2 will allow you
to
make the operation of the drive automatic (without a manual switch). Set
the
jumpers to output density on pin 2. Use this drive output to control an IC
that flip-flops the clock to pin 18 of the floppy controller. You MUST use
the proper disk, as they are what selects the density.
I used a 74F157 chip to control the clock going to the Ajax chip. It
was the easiest way I could find with the the TTL chips I had at my
disposal. The connections are minimal and simple; pin 8 to ground, pin 16
to +5v, pin 1 (strobe) to pin 2 of the drive, pin 14 to 16mhz (pin 39 of
shifter), pin 13 to 8mhz, and pin 12 to pin 18 of the Ajax (floppy cont.)
Also pin 15 must go to ground. That's the enable pin.
In the above circuit, the 157 chip will send the 16 mhz clock to the
floppy controller when a HD disk is inserted in drive A, and the drive
select for that drive goes low (selected). In all other cases, 8 mhz is
sent
to the controller. This will allow the use of both drive types on the
system.
There are many different ways to hook up drives. Make sure that you
get the jumper settings with the drive that you get. Life can be tough
without them.
Wes Newell, fidonet 1:124/7028, Atarinet 51:202/0
-!- Maximus 2.01wb
! Origin: Wylie Connection 214-442-0388 ZYX 19.2K+V32Bis (51:202/0)
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