Apple /// fdc possibility?

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Apple /// fdc possibility?

Postby rjustice » Sun Aug 31, 2014 5:40 am

I have been wondering if there was a way to use the cffa3000 floppy controller with the apple ///. I had the idea that if the internal floppy controller was disabled, then if the cffa3000 was set to slot 6, then would it work?

It turns out no, but I'll tell what I found and maybe Rich can comment if there is any chance to make this work. Not sure if this was tried during the development of the cffa3k.

The theory is that the big difference between the A3 fdc controller is the ability to select 4 drives. It does this with some additional circuitry, and the A2 1st/2nd drive select actually selects the internal or external floppies. Extra circuity then selects between external disk 1 to 3. If only 2 floppies were going to be used, ie 1 internal & 1external, then this extra circuitry could be ignored.

I did a test on my A3 by bending out pin 9 of the relevant two 74ls138 decoders. The 74ls138 at K7 is for C06X, pin 9. The 74ls138 at J6 is for C6XX, pin 9.
With the cffa3k in, it was able to read in the boot sector ok, but then gave I/O ERROR in the screen. So no luck.

I then wondered if the A3 was running in fast 2M mode. Looking at the source for the boot rom, it seems that it is. To test if this was causing problems, I disabled the ability for my a3 to switch to 2M by bending out the select pin from the 6522 (B6 pin9). With this done, I tested with the sos1.3 sys utils disk. I got the sos boot message but then it gives an error late in the boot process. I then tried the confidence test disk. This boots ok and passes the confidence test ok. So perhaps there is some hope here. Looks like the cffa3k fdc part does not like the A3 running in 2M mode.

/Rob
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Re: Apple /// fdc possibility?

Postby david__schmidt » Sun Aug 31, 2014 7:46 am

rjustice wrote:I had the idea that if the internal floppy controller was disabled, then if the cffa3000 was set to slot 6, then would it work?

It turns out no, but I'll tell what I found and maybe Rich can comment if there is any chance to make this work. Not sure if this was tried during the development of the cffa3k.

I'm not Rich, but I'll comment anyway. We definitely didn't test this during development. It would be an interesting curiosity if the CFFA3000 would work by modifying the /// hardware, but probably wouldn't be a mainstream thing to do (within the confines of the very small /// user community). Still, it's an interesting possibility in the coming years as physical drives and media become more scarce. Fortunately, the II and /// drives are very repairable...

rjustice wrote:I then wondered if the A3 was running in fast 2M mode. [...] Looks like the cffa3k fdc part does not like the A3 running in 2M mode.

That might be the case for the floppy emulation. It's not true for the SmartPort emulation. That runs fine in fast mode.
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Re: Apple /// fdc possibility?

Postby rjustice » Wed Sep 03, 2014 4:51 am

Yes, your right, would be only a very small user base compared to 3 runs of the cards that I assume nearly all went into Apple2 series computers. We are a "little" bit out numbered :-)

Thinking about what I tried, I disabled the device rom select at C6XX, this may have been why SOS did not boot as I think that might need to be ram. IF there was a way to tweak the cffa logic to run the fdc at 2M, then it would also need a dip switch to disable the device rom for the ///. This would then leave only one select line that would need to be "switched" to disable the internal floppy controller.

/Rob
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