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Old 11 September 2017, 22:11   #1
BlankVector
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Join Date: Jun 2012
Location: Paris, France
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DF0/DF1 inverter

Hello. I gladly own an A500+ with a DF0 Selector from AMIGAstore.eu (using Gotek/HxC firmware as external drive).

The description of the switch says:
When you set the switch to "ON", the external unit starts working as an internal unit. The internal unit will then be disabled.
And indeed, it works like that. I can even notice that behaviour in the early boot screen, when holding both mouse buttons on power on:
- in position OFF, I can see DF0 and DF1 as boot option.
- in position ON, I can only see DF0.

Then it continues like that in Workbench: in position ON, nothing happens when I insert a floppy in the internal drive.

Nothing wrong, as this is precisely the behaviour described in the documentation.

However...

1) Is there any way (hardware mod...) to make the internal drive appear as DF1 when the switch is in position ON? In other words, make the switch really invert DF0/DF1, not partially.

2) Incredibly, the above already works with EmuTOS! When the switch is in position ON, EmuTOS detects 2 drives, and both work
I suspect something wrong in the EmuTOS floppy driver. If DF1 is disabled for AmigaOS, it should also be the same for EmuTOS.
On the other hand, if it works fine with EmuTOS, I can't see any good reason it would not also work fine for AmigaOS.

Any hint will be welcome.
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Old 11 September 2017, 22:27   #2
Juz400
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You can do this,
I built one back in the Day, there are signal lines from the chip that you plug the DF0 selector in. One for each of the four drives you can attach.
You just need to swap a pair of lines around with a switch, its only slightly more complex than what you have now.
I would have to find a schematic to remember exactly what to do...

EDIT:
U8 (cant remember if Odd or Even CIA)

Pins
13--SEL0 (DF0)
14--SEL1 (DF1)
15--SEL2 (DF2)
16--SEL3 (DF3)

Your new switch setup just needs to swap the signal on Pins 13 and 14

Last edited by Juz400; 11 September 2017 at 22:39.
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Old 12 September 2017, 10:45   #3
Toni Wilen
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Switching select lines only makes DF1: look like DF0:. It can't make DF0: fully working DF1: if internal drive does not have built-in ID hardware. (For example A500 do not have it).

DF0: internal drive always returns "no drive" ID if drive without ID hardware. KS ROM ignores it and always assumes 3.5"DD, even if drive is not connected.

External drives are only detected and accepted if correct 3.5"DD (or 3.5"HD) ID is returned when queried.

EDIT: Does emutos detect the drive by attempting to seek and testing track0? Ignoring the ID signal?
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Old 13 September 2017, 12:03   #4
BlankVector
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Many thanks for your hints, that makes sense.
I will check EmuTOS sources and report back.
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