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Old 09 May 2011, 18:48   #1
wallmaker84
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External Floppy schematics

Dear all,
I would to make myself an external floppy cable / board. I have a spare chinon floppy drive and i would able to use it with my A600 / A1200 as DF1...perhaps in the future i will buy an HxC floppy emulator and i will not to renounce to my floppy drive...I'm asking (after a walk around on the net and forums) if anyone have the schematics for one of these external driver or anyone has realized a similar project on the past...
I'm waiting for any kind of advice...
Thank you to all!!!
Long life to Amiga...
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Old 09 May 2011, 20:44   #2
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Aminet has several. Look in docs/hard.
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Old 09 May 2011, 21:00   #3
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Thank you Jope...i have found just only one archive (http://aminet.net/package/docs/hard/PCDrive) It is concerning about PC-IBM floppy drive, i'm afraid it doesn't work for my amiga floppy drive as it is...
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Old 09 May 2011, 21:08   #4
prowler
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It should not be difficult to work out how to interface an external Amiga floppy drive with your Amiga's external floppy port from the pin assignments if you only require the unit to operate as DF1:

The logic on the external floppy interface is required only if you need a passthrough connection for additional drives.
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Old 09 May 2011, 23:32   #5
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So if i want only 1 external drive operating as DF1: the only things to do is to right wire Disk port on amiga and the pins on rear of disk drive?
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Old 09 May 2011, 23:34   #6
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Yes, but you will only need to wire up DB23 Pin 21 /SEL1 (Select Drive 1) to address the drive as DF1: Not Pins 9 or 20 (Select Drives 2 and 3, respectively).
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Old 09 May 2011, 23:43   #7
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Good, as soon i can i will try this task....thank you
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Old 09 May 2011, 23:46   #8
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Good luck, and please let us know how it goes.
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Old 10 May 2011, 08:30   #9
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Quote:
Originally Posted by prowler View Post
The logic on the external floppy interface is required only if you need a passthrough connection for additional drives.
It is needed in any case. Basically the two logic chips act as a memory for the motor signal and IIRC also as a source for the RDY ID pulse.

The Amiga only has one motor control signal (unlike the PC which has two), so the motors are turned on by enabling select and motor at the same time. This status is then remembered in the logic and the motor stays on even if the machine wants to read from a different drive.

The passthrough port in the external drives passes everything else through except for the drive selects, the lowest of which goes to the drive mechanism and the rest are shifted down by one and go to the passthrough port.

Amiga 500 floppy port:
21-DS1 9-DS2 20-DS3
First drive floppy port:
21-DS2 9-DS3 20-NC
Second drive floppy port:
21-DS3 9-NC 20-NC
Third drive floppy port:
21-NC 9-NC 20-NC

And as you can see, there are no selects left so if you plug in a fourth extra drive, it won't do anything.

Now original poster, go and read all of the different "add floppy drive" docs in docs/hard and build it. :-) You don't even need a PCB, just vero board and lots of wire. :-)
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Old 10 May 2011, 13:05   #10
RedskullDC
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Hi Wallmaker84, et al.

Quote:
Originally Posted by wallmaker84 View Post
Dear all,
I would to make myself an external floppy cable / board. I have a spare chinon floppy drive and i would able to use it with my A600 / A1200 as DF1...perhaps in the future i will buy an HxC floppy emulator and i will not to renounce to my floppy drive...I'm asking (after a walk around on the net and forums) if anyone have the schematics for one of these external driver or anyone has realized a similar project on the past...
I'm waiting for any kind of advice...
Thank you to all!!!
Long life to Amiga...
The Abacus "Amiga System Programmers Guide" book has a schematic for an extaernal drive on page #51.

I had no trouble finding a PDF copy of the book online using a google search.

The relevant schematic is attached here, though I recommend reading the book as it details the signals rather well.

Hope this helps,
Red
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Old 10 May 2011, 13:30   #11
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http://aminet.net/docs/hard/floppyint.lha

Not sure if that would work properly for two drives, it might run both motors at the same time even if you're only reading from one. Hence I recommend using it only to control one drive.

The 74ls74 flip flop has two flip flops in it and the 74ls38 nand gate has four nand gates in it, so you can adapt it to two separately controlled mechanisms pretty easily without increasing the part count.

Last edited by Jope; 10 May 2011 at 13:41.
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Old 10 May 2011, 20:08   #12
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Fantastic!thank you to all...i'm preparing an university exam so at time i haven't much spare time to develop these schematics (and also play with my amiga )..when i find one hour i will start to develop something...
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Old 10 May 2011, 20:16   #13
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Quote:
Originally Posted by Jope View Post
Quote:
Originally Posted by prowler View Post
The logic on the external floppy interface is required only if you need a passthrough connection for additional drives.
It is needed in any case. Basically the two logic chips act as a memory for the motor signal and IIRC also as a source for the RDY ID pulse.

The Amiga only has one motor control signal (unlike the PC which has two), so the motors are turned on by enabling select and motor at the same time. This status is then remembered in the logic and the motor stays on even if the machine wants to read from a different drive.
I stand corrected. Thanks for the info, Jope.

Even relatively experienced Amiga users can learn something new every day on EAB!
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Old 10 May 2011, 21:40   #14
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@RedSkullDC

There is an error in the schematic from the 'Amiga System Programmers Guide'
The inputs to NAND gate N1 should connect to pin 21 (SEL1) not DIR as shown, otherwise the external drive will only be selected when the drive head moves in the right direction.

This modified circuit is also required with my original PC floppy drive adaptors. The logic to do this is included in the new (in development) ones.

Ian
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Old 11 May 2011, 08:51   #15
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Stedy, can you verify whether _RDY should be connected directly to the drive in a generic DD external drive setup?
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Old 11 May 2011, 09:17   #16
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I have found the book!In a site very very nice...this afternoon during a break i take a look at it! BTW floppyint.lha refer also to a modification compatible with Amiga drives or only IBM drives?
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Old 11 May 2011, 10:33   #17
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Quote:
Originally Posted by wallmaker84 View Post
I have found the book!In a site very very nice...this afternoon during a break i take a look at it! BTW floppyint.lha refer also to a modification compatible with Amiga drives or only IBM drives?
floppyint.lha is for Amiga compatible drives.

If you want to use a PC drive with it, you must modify the drive to be Amiga compatible.

See:
http://eab.abime.net/showthread.php?t=30944
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Old 11 May 2011, 23:51   #18
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Quote:
Originally Posted by Jope View Post
Stedy, can you verify whether _RDY should be connected directly to the drive in a generic DD external drive setup?
If it is a Chinon drive, as used by the Amiga, nRDY can be connected directly. If it is a PC drive, the circuit posted by RedskullDC (with the SEL1 correction) is required to generate the nRDY signal.

Have tested this myself a while back, worked fine.

Ian
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Old 12 May 2011, 13:36   #19
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So for my chinon i can avoid all the wires incoming and outgoing the N2 gate?
Daniele
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Old 12 May 2011, 14:10   #20
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i have a roctec, use normal drive for pc but 26 pin, not 34
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