131 lines
6.7 KiB
Plaintext
131 lines
6.7 KiB
Plaintext
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The Control Team proudly presents:
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Zaphod Beeblebrox's notes on using Pc 1.44 Mb 3.5" drives with ST/STE's with a
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minimum of trouble. If you have Tos v2.06 and STE, even the TOS will recognize
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that you have an 1.44 drive installed as your internal drive!!! Version 1.1
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==============================================================================
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This whole thing started a few days ago, when I decided that I was fed-up with
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all those 720 Kb disks, I needed something better for backing up all the wares
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from my BBS, and I thought.... Hmm, wait a sec, the Pc dudes have 1.44 drives
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in their computers, and so does the Mega STE.... Why not install one in my
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"normal" STE as well??? Then I started planning for the project, and came to
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this conclusion:
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1. You must have a WD1772-02-02, the other ones will not handle the doubled
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clock frequency of 16 mHz without problems.
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2. Your 1.44 Mb diskdrive must output a signal on pin 2 (HD detect) whenever a
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HD disk is present in the drive. Examples of drives that works fine with this
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modification: TEAC and Panasonic. I used a Panasonic drive for my own
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computer. Not all drives have the jumpers set-up correctly when you buy them,
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so *NEVER* buy a drive if they cannot tell you fer sure that it really has the
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HD detect signal output. Because if it doesn't have it, you're fucked up!!
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3. You must have some kind of circuit that only enables 16 mHz when drive 0 is
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selected and a HD disk is present in drive 0.......
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4. If you have a STE, you should also solder a jumper on bridge E6 underneath
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the drive in order to get TOS to recognize that you have a 1.44 Mb drive.
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The Circuit:
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============
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I designed my automatical HD detect switch around a 74LS00 and a 74F157. The
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LS00 is a quadruple NAND gate, and the F157 is a dual two-to-one multiplexer.
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The first thing you need to do, is to invert the HD detect signal with one of
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the NAND gates, you simply feed the HD detect on both inputs of one of the
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NAND gates and there you have it - inverted HD detect on the output of that
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NAND gate!!!! What you do now, is that you take the drive B select signal and
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the inverted HD detect signal and feed them onto the inputs of a second NAND
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gate. Now, you'll only get a '0' output from the second NAND gate if....
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* Drive B is not selected
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* Drive A contains a HD disk
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After this, we simly feed the output of the second nand gate to the select
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input on the F157 multiplexer. This means that the conditions above will
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select 16 mHz clock for the FDC, and all other conditions will select the
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standard 8 mHz clock. Easy, isn't it??? Now, I will present you with the
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actual circuitry.... Remember that the wires are only joined where I have "+"
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signs, other wires are just crossing each other. It's very importanf that you
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get tha 74F157 and not anything slower. the 74LS157 cannot handle more than
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about 14-15 mHz and we need something that will switch 16 mHz without problems.
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+--------+ +-----------------------+
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| | | |
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| | | | | | | | | |
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| -------------------------- |
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| ! ! |
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| ! ! |
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| \ 74F157 ! |
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| / MULTIPLEXER ! |
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| ! ! |
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| ! ! |
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| -------------------------- |
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| | | | | | | | | |
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| +----+ | | | +-+---+
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| | | | | |
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| | | | +---------------------------+
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+---|----+ | +--------------------------+ |
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| | | | | | |
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| | | +-------------------------+ | |
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| | | | | | |
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| | ----------------------- | | | |
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| | ! ! | | | |
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| | ! ! | | | |
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| | \ 74LS00 ! | | | |
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| | / QUAD NAND GATE ! | | | |
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| | ! ! | | | |
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| | ! ! | | | |
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| | ----------------------- | | | |
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| | | | | | | | | | | | |
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| | | | | +--+ | +----+ | | |
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| | | | | | | | | | |
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| | | +--|--------+ | | | |
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| | | | | | | | |
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| +----------+ | | | | |
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* * * * * * *
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+5V D1S HDD GND 16M 8M FDC
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What do all these abbreviations stand for?? Well....
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+5V is the juice required for our little gadget... Get this from Pin 15 of the
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WD1772-02-02 chip.... GND is ground, which you can get from Pin 14 of the
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WD1772-02-02... D1S is drive B select, which is Pin 19 of the YM2149
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soundchip. HDD is pin 2 of the diskdrive ribbon cable. It's the wire right
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besides the red marked wire, which is number one. That is, HD detect is wire
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#2 on the 34 wire diskdrive ribbon cable. 16M is a 16 mHz signal, which can be
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tapped from Pin 52 of the STE videoshifter, or Pin 2 of the STE MCGLUE (The
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big 144 pin surface mounted, not a very good idea, but if you follow the trace
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from Pin 2 of it, you'll discover the correct thru-hole where you should tap
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the 16 mHz signal, it's located right between the videoshifter and the SIMM
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memory modules on the motherboard). FDC is the WD1772 clock signal, which can
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be found on Pin 18 of the Floppydisk controller. 8M is the 8 mHz signal, which
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can be tapped from the old pin 18 hole, or a thru-hole near the WD1772 socket.
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Or you might also tap the 8 mHz signal from pin 15 of the MC68000 CPU.
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This has been another Control Team production, presented to you by Zaphod
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Beeblebrox of The Control Team. This project worked just fine for me, but I
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will not accept any responsibility if your computer turns itself into a
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toaster while performing this hardware modification. By the way, if you like
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my work, you're welcome to send me a donation if you want to... (HAHAHAHA!!!).
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You can reach me at any of the Control Team boards:
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Eagles Nest BBS +46-18-262804 (235 Megs and HST Dual Standard).
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Data Control I. +1-(818)/558-5636 (200 Megs + 88*x Syquest and HST).
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Or send me a snailmail at this address:
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Carl Andersson
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Liggargatan 5J
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754 20 Uppsala
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Sweden
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