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11.3 HD Disk ST
High Density Disk Drive Modification by Randy Kwak
What you need:
- CO25914 (Video Shifter Chip) contained by every Atari ST
N.B. If your floppy controller chip is the older
"00-02", it will
- HD floppy drive
Desolder pin 18 ("clock") of your drive controller chip
and bend it up and out of the hole. Solder a wire to it. Connnecting
the wire to the (now empty) hole gives you an 8 MHz clock (double
density). Connecting the wire to pin 39 ("16 MHz out") of
the video shifter chip gives you a 16 MHz clock (high density).
I have installed a toggle to switch between 8 MHz and 16 MHz.
8 MHz ____
(now empty) hole -> o----------| | /
| | / ______ 16 MHz
|----------| |/ | |
|_|_|_|_|_|_|_|_|_|_|_|_|_| _| | | _|_|_|_|_|_|_|_|_|_|_|_
| * | | |____| | | *
|> WD 1772 02-02 | | switch | |> CO25914
|___________________________| |____________| |_______________________
| | | | | | | | | | | | | | | | | | | | | | | | |
Formatting programs:
- Diamond Format (HD 3 1/2", 18 & 20 sectors per track,
IBM boot sector)
Note that the normal formatting routine from the desktop will only
give you DSDD disks. This is because the HD formatting routine was not
built into TOS until TOS 2.6. You *MUST* use a software formatter or
have pre-formatted disks.
Problems you may encounter: "Damage on drive XX; check
connections.."
- On 3 1/2" floppies, change step rate for drive to 6ms or
12ms (Double Click's "Floppy Configurator" is great for
this). Reason: when you double the clock rate, the step rate is
halved.
- On 5 1/4" disk drives, change step rate for drive.
Additionally, you may need to construct an interface to provide the
necessary logic and buffering for the drive select and motor on
signals. (1997 note: I can dig this out if anyone is interested).
Modification for 1.44 MB Floppydisk
This whole thing started a few days ago, when I decided that I was
fed-up with all those 720 Kb disks, I needed something better for
backing up all the wares from my BBS, and I thought.... Hmm, wait a
sec, the Pc dudes have 1.44 drives in their computers, and so does the
Mega STE.... Why not install one in my "normal" STE as
well??? Then I started planning for the project, and came to this
conclusion:
1.
2.
3.
4.
The Circuit:
I designed my automatical HD detect switch around a 74LS00 and a
74F157. The LS00 is a quadruple NAND gate, and the F157 is a dual
two-to-one multiplexer. The first thing you need to do, is to invert
the HD detect signal with one of the NAND gates, you simply feed the
HD detect on both inputs of one of the NAND gates and there you have
it - inverted HD detect on the output of that NAND gate!!!! What you
do now, is that you take the drive B select signal and the inverted HD
detect signal and feed them onto the inputs of a second NAND gate.
Now, you'll only get a '0' output from the second NAND gate if
* Drive B is not selected
After this, we simly feed the output of the second nand gate to
the select input on the F157 multiplexer. This means that the
conditions above will select 16 mHz clock for the FDC, and all other
conditions will select the standard 8 mHz clock. Easy, isn't it???
Now, I will present you with the actual circuitry.... Remember that
the wires are only joined where I have "+" signs, other
wires are just crossing each other. It's very importanf that you get
tha 74F157 and not anything slower. the 74LS157 cannot handle more
than about 14-15 mHz and we need something that will switch 16 mHz
without problems.
+--------+ +-----------------------+
| | | |
| | | | | | | | | |
| -------------------------- |
| ! ! |
| ! ! |
| \ 74F157 ! |
| / MULTIPLEXER ! |
| ! ! |
| ! ! |
| -------------------------- |
| | | | | | | | | |
| +----+ | | | +-+---+
| | | | | |
| | | | +---------------------------+
| | | | | |
+---|----+ | +--------------------------+ |
| | | | | | |
| | | +-------------------------+ | |
| | | | | | |
| | | | | | | | | | | | |
| | ----------------------- | | | |
| | ! ! | | | |
| | ! ! | | | |
| | \ 74LS00 ! | | | |
| | / QUAD NAND GATE ! | | | |
| | ! ! | | | |
| | ! ! | | | |
| | ----------------------- | | | |
| | | | | | | | | | | | |
| | | | | +--+ | +----+ | | |
| | | | | | | | | | |
| | | +--|--------+ | | | |
| | | | | | | | |
| +----------+ | | | | |
| | | | | | |
| | | | | | |
* * * * * * *
+5V D1S HDD GND 16M 8M FDC
What do all these abbreviations stand for?? Well....
This has been another Control Team production, presented to you by
Zaphod Beeblebrox of The Control Team. This project worked just fine
for me, but I will not accept any responsibility if your computer
turns itself into a toaster while performing this hardware
modification. By the way, if you like my work, you're welcome to send
me a donation if you want to... (HAHAHAHA!!!). You can reach me at any
of the Control Team boards:
Eagles Nest BBS +46-18-262804 (235 Megs and HST Dual Standard).
Or send me a snailmail at this address:
Carl Andersson
Copyright © Robert Schaffner (doit@doitarchive.de) Letzte Aktualisierung am 23. Mai 2004 |
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