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Old 24 November 2017, 13:09   #1
Lurch_AU
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DIY A500 Boot Selector

Floppy Disk Boot Select Switcher

I made this modification to be able to boot from an EXTERNAL Floppy Drive on an Amiga 500. The external drive actually being a Gotek Floppy Drive Emulator that uses a USB Thumb Drive to load Amiga Disk image files (.ADF files).

By default, an Amiga (running KickStart 1.3) cannot boot to an external Floppy Disk Drive, it can only boot from DF:0 (the internal drive) and although in theory you could boot off a KS 1.3 Disk and then start a game from KickStart, most games are hard coded to run from DF:0.

So the trick is to turn the external drive into DF:0.

Please note that when this modification is switched to the external drive, the internal drive is NOT operational and cannot be used.

Please also note that, yes – these images are Photoshopped as it makes it clearer, but also, I built mine on the fly and not taking photos.

Please also ALSO note – I make no guarantees that this will work for you and that your Amiga won’t go ‘Pffft’, the world implodes, your cat leaves you, or Donald Trump becomes President (wait…. Shit!)

Final Note: Do NOT operate the switch while the machine is powered on. Your machine won't like it.

Requirements:
- 3x 40-pin IC Sockets (note: you want 1x the cheap “blade” style, and 2x the better “pin” style, this will become apparent later.
- A 2-way, 6-pin switch
- Wire (I used Orange, Yellow, Blue and Green. Use whatever, but just remember which wire goes where as I’ll be explaining it using these colours)

For the Gotek:
- And External Amiga Floppy Disk Drive (or at least the chassis for one)
- A Gotek Drive
- A thumb drive with the required Gotek files and the ADF files you want to run.

Step one:
Take the “blade” IC socket and carefully bend out pins 13 and 14



Step Two:
Solder the Orange wire to Pin 13 and the Yellow wire to Pin 14.



Step 3:
Take one of your “pin” style IC Sockets.
Solder the Green wire to the TOP of Pin 13 and the Blue wire to the TOP of Pin 14

This is why we use the “pin” style here as its WAY easier to solder to the top of, but the “blade” ones are easier to bend the pins on.



Step 4:
Take the third IC socket and CUT OUT pins 13 and 14. I used a small pair of side cutters.



Step 5:
Now carefully place all three sockets together in this order…. (from top to bottom)
  • First IC you made (Orange and Yellow Wires)
  • The LAST socket you made (the one with the pins cut out)
  • The Second IC socket (Green and Blue wires).
If should look something like….. (note, this image has been turned around)
AKA: “The Socket Tower”, or the “Tower o’ Socket”



Step 6:
The Switch.
For our purposes, the Switch Basically has 2 pairs of “In” and one pair of “Out”



Step 7:
Solder the wires from the Socket “Tower” we just built, to the switch as follows:
  • Orange to Pin 1 on the switch
  • Yellow to Pin 2 on the switch
  • Green to Pin 3 on the switch
  • Blue to Pin 4 on the switch



Step 8:
Now, take a small piece of Orange Wire, and loop from Pin 1 to Pin 6



Step 9:
Take a small piece of Yellow Wire, and loop from Pin 2 to Pin 5



Step 10:
It’s now time to install the Socket Tower.
Carefully remove the Even CIA chip from your Amiga’s mother board
(Tip, unplug and move out of the way the Internal Drives ribbon cable and power cable)
Place your Socket Tower in where the Even CIA chip just came from.
Take note of the ‘Notch’ and line it up with the socket on the motherboard. All your wiring should point towards the floppy drive ribbon cable plug/pins on the mother board.
Now place the Even CIA chip back in on top of the tower.
(Note: Mine fit fine, but others have said the RF Shield pushes down on the Even CIA chip more than they’d like; so be prepared to pull out your Dremel tool and cut a hole directly above your new “Tower of Socket” in the shield)



Step 11:
Mounting the switch.
Honestly, mount the switch where you want. Some people are known to just run it down to the Trap Door and access it this way.
I removed the warning sticker and mounted mine here (requires a 6.5mm drilled hole)



Finish up and Testing
Finally, put your Amiga back together.
Depending on which way around you mounted your switch:
One direction should give you…
- Internal Drive working fine.
- External Drive comes up as DF:1
The other direction will give you:
- External Drive becomes DF:0 and is bootable
- Internal Drive is inoperable.
I hope it all works for you, and best of luck.
- Lurch

Here is a PDF version of this How-To: https://1drv.ms/b/s!AoKV6tTzOYOVvhdSI3y55J6hJ2zy

Last edited by Lurch_AU; 25 November 2017 at 01:17.
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Old 24 November 2017, 13:40   #2
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Nice, but would be good if you could also post it in the thread too, then people could discuss without having to download it
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Old 24 November 2017, 13:43   #3
Lurch_AU
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Sorry, I put the PDF together for a friend; so dont have all the photos online.
If I get time to re-write it, i can.
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Old 24 November 2017, 13:47   #4
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I can extract it all to .doc or .docx (MS Word) for you if you want, then you can fumble around and re-write it here, if that's any help?
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Old 24 November 2017, 14:14   #5
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Done
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Old 24 November 2017, 14:26   #6
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Haha! You beat me to it, just posted it and overwrote yours, so I have restored it back

Good work
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Old 24 November 2017, 14:49   #7
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Not a hassle.
Not sure if it's sticky-worthy; but its a pretty easy, simple, and cheap, but effective mod.
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Old 24 November 2017, 14:53   #8
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Quote:
Originally Posted by Lurch_AU View Post
Not a hassle.
Not sure if it's sticky-worthy; but its a pretty easy, simple, and cheap, but effective mod.
I'll let Jope decide, he's the Hardware mods mod and he'll know better than I will
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Old 24 November 2017, 16:18   #9
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Hi Lurch,
that's a pretty neat method for boot selection you have designed for the A500's thanks very much for sharing it with us, it's something worth doing for ease of use with the Gotek's booting as an external unit.
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Old 24 November 2017, 17:12   #10
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Very nice
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Old 24 November 2017, 18:38   #11
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I do like the concept and would consider now for my A500.

Question - can you switch drives while the Amiga powered on for flexibility? Or is it strictly only while powered off?

I guess it has to be powered off.
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Old 24 November 2017, 18:51   #12
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Quote:
Originally Posted by BrooksterMax View Post
I do like the concept and would consider now for my A500.

Question - can you switch drives while the Amiga powered on for flexibility? Or is it strictly only while powered off?

I guess it has to be powered off.
Although the most obvious answer to this would be "only switch it while your Amiga is switched off" and most people would follow that side of common sense, unfortunately not everyone would apply that degree of sense.

Therefore, it would be a good idea to make that statement very clear at the end of the instructions
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Old 25 November 2017, 00:15   #13
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Good point. And yes, ONLY when the machine is powered off. I did it once with t on. Didn't break anything but the machine certainly didn't like it.

Warning added.
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Old 27 November 2017, 13:09   #14
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Seems there was a demand for this. The method has been discussed many times in writing (I've explained it a few times myself), but nothing beats a bunch of pictures.

Could you elaborate for our viewers how a boot selector works, please? I'll then stick it.

IMO this sentence is a good place to expand on:
>So the trick is to turn the external drive into DF0:.

It is a good tutorial, but I want people to know how the modification achieves the result. Who knows, it might inspire someone to delve deeper into these things.
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Old 29 December 2017, 21:48   #15
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I've done this very same modification following another tutorial, but nice one anyway! It's pretty easy to understand how it works: pins 13-16 of the even CIA chip are the selection lines for drives DF0-DF3:, in that order.

This mod simply swaps pin 13 with pin 14, so when the CIA chip thinks it's accessing DF0:, it will access DF1: instead, and vice-versea.

This means that Amiga's internal drive should appear as DF1:, but it actually won't, it will just be sitting there. The reason for this is more complex, I once found a detailed explanation for it, but I don't have it handy. IIRC, it had something to do with the Amiga interrogating drives at power up to see what model they are (think 3.5" or 5.25"), but it doesn't do that for the internal drive, since that will always be a 3.5" drive. When it becomes DF1:, it should answer that request, but it seems they didn't include the actual circuitry, so it will never reply and the Amiga won't just see it. I think it is possible to build the missing circuit, but I will have to find the original post for that.

Without the missing circuit, step #8 can be safely skipped, since the internal drive will be unusable anyway.

Hope it helps .

Last edited by SukkoPera; 29 December 2017 at 22:30.
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Old 29 December 2017, 21:53   #16
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Sure, but I was hoping for the original poster to edit their post with that info. I didn't want to start editing it myself, as I thought that might be a bit rude.
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Old 29 December 2017, 22:08   #17
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Sorry for spoiling that then .

Anyway, I've found the post I was referring to, it's this one: http://www.amiga.org/forums/showpost...23&postcount=4.

A more hackish way of "fixing" the internal drive is here: http://www.amibay.com/showthread.php...l=1#post716492. It's basically the same method as the other thread, just with a "wired or" instead of a proper OR gate.

I will test the latter, one day .

Last edited by SukkoPera; 30 December 2017 at 02:15.
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Old 29 December 2017, 22:23   #18
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Heh, nothing spoiled, it will help others here, as the thread is not yet stuck. :-)

This is just the "no blind tutorials" person that I am.. A tutorial is ok, but it must also explain what you are actually doing instead of telling "connect pin x to pin y" without any reasons. :-)
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Old 16 January 2018, 22:37   #19
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Hi all, this is my first post here. I'm Martijn from NL, I got an A500 when I was young, then later got an A1200 and gave the A500 away. I sold my A1200 some 15 years ago, and then some years back I bought back and A500, mostly to play Sensible Soccer again. :-) Just got that A500 back out of its box and upgraded it with a Gotek in an external enclosure (funny how adding the piezo buzzer to the Gotek makes it feel more real) and a boot selector.

Quote:
Originally Posted by SukkoPera View Post
Anyway, I've found the post I was referring to, it's this one: http://www.amiga.org/forums/showpost...23&postcount=4.

A more hackish way of "fixing" the internal drive is here: http://www.amibay.com/showthread.php...l=1#post716492. It's basically the same method as the other thread, just with a "wired or" instead of a proper OR gate.
These posts are actually by the same person. Somewhere later in the first thread he also mentions that it can be done with just a couple of diodes and a resistor.

Quote:
Originally Posted by SukkoPera View Post
I will test the latter, one day .
I will test it later this week, already have the A500 opened up, waiting for the components to arrive.

I followed some tracks on the motherboard, checked the schematics and think I can connect the following:
U36 pin 5 (=Gary 46) diode to Internal floppy #34 (= Odd CIA 7)
Even CIA pin 13 (=Gary 16) diode to Internal floppy #34 (=Odd CIA 7)

U36, Even CIA and Internal floppy are closer together than Gary, Even CIA and Odd CIA, so this would keep it a little neater I think.

Last edited by Martijn; 16 January 2018 at 22:56.
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Old Yesterday, 01:56   #20
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BTW, If you turn on the Amiga with the switch in the "normal" position (df0 internal and df1 external) and then let kickstart come all the way up, then flip switch them and insert disks, then both drives will still work swapped.

It will not hurt anything to switch while powered on as long as there is nothing in the drives when you do it.
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