Use a PC 1.44 Mb 3.5" drives with an Atari ST/STE
The Control Team proudly presents:
Zaphod Beeblebrox's notes on using Pc 1.44 Mb 3.5" drives with ST/STE's with a minimum of trouble. If you have Tos v2.06 and STE, even the TOS will recognize that you have an 1.44 drive installed as your internal drive!!! Version 1.1
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:
- You must have a WD1772-02-02, the other ones will not handle the doubled clock frequency of 16 mHz without problems.
- Your 1.44 Mb diskdrive must output a signal on pin 2 (HD detect) whenever a HD disk is present in the drive. Examples of drives that works fine with this modification: TEAC and Panasonic. I used a Panasonic drive for my own computer. Not all drives have the jumpers set-up correctly when you buy them, so *NEVER* buy a drive if they cannot tell you fer sure that it really has the HD detect signal output. Because if it doesn't have it, you're fucked up!!
- You must have some kind of circuit that only enables 16 mHz when drive 0 is selected and a HD disk is present in drive 0.......
- If you have a STE, you should also solder a jumper on bridge E6 underneath the drive in order to get TOS to recognize that you have a 1.44 Mb drive.
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
- Drive A contains a HD disk
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....
+5V is the juice required for our little gadget... Get this from Pin 15 of the WD1772-02-02 chip.... GND is ground, which you can get from Pin 14 of the WD1772-02-02... D1S is drive B select, which is Pin 19 of the YM2149 soundchip. HDD is pin 2 of the diskdrive ribbon cable. It's the wire right besides the red marked wire, which is number one. That is, HD detect is wire #2 on the 34 wire diskdrive ribbon cable. 16M is a 16 mHz signal, which can be tapped from Pin 52 of the STE videoshifter, or Pin 2 of the STE MCGLUE (The big 144 pin surface mounted, not a very good idea, but if you follow the trace from Pin 2 of it, you'll discover the correct thru-hole where you should tap the 16 mHz signal, it's located right between the videoshifter and the SIMM memory modules on the motherboard). FDC is the WD1772 clock signal, which can be found on Pin 18 of the Floppydisk controller. 8M is the 8 mHz signal, which can be tapped from the old pin 18 hole, or a thru-hole near the WD1772 socket.
Or you might also tap the 8 mHz signal from pin 15 of the MC68000 CPU.
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).
- Data Control I. +1-(818)/558-5636 (200 Megs + 88*x Syquest and HST).
Or send me a snailmail at this address:
Carl Andersson
Liggargatan 5J
754 20 Uppsala
Sweden
