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Re: On attempting to make the 3.5" floppy adaptor to work...
Michael J. Mahon wrote:
> Tristan Mumford wrote:
>> Michael J. Mahon wrote:
>>
>>
>>>Tristan Mumford wrote:
>>>
>>>>Michael J. Mahon wrote:
>>>>
>>>>
>>>>
>>>>>Michael J. Mahon wrote:
>>>>>
>>>>>
>>>>>>Tristan Mumford wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>G'day.
>>>>>>>
>>>>>>>As you may or may not know I've been working on a little device to
>>>>>>>allow PC
>>>>>>>3-1/2" floppy drives to be used on a disk ][.
>>>>>>>
>>>>>>>It can now do the following:
>>>>>>>
>>>>>>>* de/Select and spin up/down the drive.
>>>>>>>* Detect the write-protect state of an inserted floppy.
>>>>>>>* Move the head around.
>>>>>>>
>>>>>>>What it can't seem to do is read and write. The basic question I want
>>>>>>>to ask
>>>>>>>is whether the apple2 has an active high or low for read and write
>>>>>>>pulses.
>>>>>>>I believe it's active high, but I'm starting to doubt myself a
>>>>>>>little.
>>>>>>
>>>>>>
>>>>
>>>>
>>>>
>>>>>>Actually, it's *neither*! The Disk ][ Controller *toggles* the state
>>>>>>of the write line each time that it writes a "1". No toggle = "0".
>>>>
>>>>
>>>>So are you saying instead of the PC floppy dataline pulsing the data low
>>>>for a phase change, the disk ii analog card just changes state and stays
>>>>that way until the next phase change?
>>
>>
>>>The WRITE DATA line stays whichever way it is until the next "1" (which
>>>is the next flux reversal).
>>>
>>>(I find using "phase" in this context confusing, since the head stepper
>>>is positioned using "phase" signals.)
>>
>>
>> Because I had to "upgrade" to the bigger uC, it also ended up with a
>> 12MHz crystal driving it. Because it only involved very minor work I
>> decided to send the write signal via the uC to change it from flux
>> reversals to pulses.
>> It's probably too slow to do it though. It didn't work. Or maybe it's
>> reading it back via the hex inverter that didn't work.
>> Unless I misunderstood UTA2's section on the disk ii, the controller card
>> gets data from the drive in a series of 1uS, active high pulses, which
>> apart from the inverted state seems to be compatible with PC floppy drive
>> standards.
>
> That sounds right.
>
>> I also managed to turn an 18f452 into a nice heating element. When I did
>> the reshuffling I managed to short the -12v to one of its IO lines, which
>> would have resulted in a nice 17v potential difference inside the chip.
>> Or is it 16v. Doesn't matter anyway. Now I have something to throw at the
>> neighbours cats.
>
> Aaaack. ;-(
I believe I measured a whopping 12ohm resistance between Vdd and Vss.
Paranoia now has me keeping my finger on top of the uC the whole time it's
on feeling for a temperature difference.
>
> Just the other day, I found an Apple ][+ ROM (the E8 ROM) that is
> a near short from +5v to ground--it also makes a nice heating element!
>
> This is the first time I've found a ROM with this failure mode.
Was the extent of the failure isolated to the ROM? I'm surprised too that it
died. Electronics don't come much more robust than a ROM.
>
>> I just want this silly thing to work. Using a touch of modern embedded
>> processing the task should be trivial.
>> That and I plain don't like when things don't work.
>>
>> On one final note, I think I _may_ have some of those PC floppy
>> controller tape drives and unopened tapes in the shed. I can't remember
>> if I sold them. I think it would be kind of fun to get them working with
>> a custom driver. A //e with a 250mb (capacity probably vastly reduced for
>> apple) tape drive. What an odd idea.
>>
>> So, am I heading in the wrong direction?
>
> It all sounds like good fun to me. ;-)
Glad you think so. Do you think that using a soft encoding method like I
attempted is wrong? I have my doubts about it. It's just it was easy to
modify my board to try it so I did.
To do it I disconnected my erroneous connection of the write signal from the
hex inverter and connected it to the uC. I also connected a pin of the uC
to the write enable pin so I could get feedback on when it wants to write.
Speaking of good fun... Today the lot of 3 SCSI cards I won on eBay for the
princely sum of $2 arrived. Two of them are memory mapped 8-bit ISA cards.
I'm sure I can find a use for them.
Sorry if this post is a little vague, but it's been a very long day. But I'm
home safely again. That's a relief :)
Tristan.
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