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Re: How much of a ][ is needed to twitch?
Alex Freed wrote:
> "Tristan Mumford" <xtristan.xmumford@xgmail.xcom> wrote in message
> news:45d27df0$0$52924$c30e37c6@lon-reader.news.telstra.net...
>> concern. With the uC running at a decent speed, and the much shorter step
>> time of the 3-1/2" drives it looks to be quite possible to use an
>> inexpensive uC to control the head.
>
> You can do just about anything with a uC. And it doesn't matter how tight
> the code is as a disk drive is a very slow mechanical device.
That is indeed true. But it seems as though the disk ii has a certain delay
time that it waits during phase changes to allow the motor to move, and
head to move etc. After that time it expects the head to be in the new
position.
So I essentially have a small but very usable delay as long as my code isn't
too sloppy. So I've avoided loops and such in my code. It is still written
in C, but in a manner which will convert to fastish code.
My device is relatively stupid. Ie it can (will) to the following:
* Translate phases to direction and step.
* Stop the head on track 0 and 80.
* in 160 track linear mode, tracks > 80 change state of /SIDE1, and reverse
step direction. (note: head does not move during 79 <->80 transition).
The ode for all that is pretty much complete. I just haven't bothered
finishing it yet.
I found out what was wrong with the uC-less part of the adaptor just now. It
seems like I had one of my common attacks of lysdexia. I had the odd and
even pins reversed on the PC floppy connector. Ie 1 = 2, 33 = 34.
It should only take me a few minutes to fix. I just need to suck up the
bridging solder for the earths, move the connected signals, and resolder
the earth bridges.
Once fixed it should be able to read track 0 (just garbage), maybe write to
it, select the drive, start and stop it, and check write protection.
It'd be nice to be able to format just that track enough to put a small
bootblock program there for testing.
>>
>> My method may. Unless I'm wrong about one aspect of the PC floppy drives.
>> I
>> believe that one strobe of /STEP (ie high, low, high) results in a single
>> track step. When it's held low it does a half step. Of course I may be
>> wrong and it may be a full step, and the strobe does two. It's hard to
>> find
>> low level detail on the workings of the drives.
>
> I don't think that is the case. I'm pretty sure that one pulse is one
> step. If you want to use all 80 tracks, you can't get half-tracks.
Oh well. No big deal unless one wants to do some kind of protected image
dump. If that's the case then it would also be dead easy to have a 40 (or
80 track using both sides of the disk) halftrack mode. Or for the really
horrible things I guess a 40 track dualside 1/4 track. I just hope nothing
of that manner exists.
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