The *meow* auction we've all been waiting for *meow*

dwight elvey dkelvey at hotmail.com
Wed Dec 27 00:15:38 CST 2006




>From: "Chuck Guzis" <cclist at sydex.com>
>
>On 26 Dec 2006 at 12:09, dwight elvey wrote:
>
> > I'm not sure why the designer of this circuit used buffers on 4 of
> > the signals? I'd think these could be just directly wired. It does
> > require that the drive be 720KB compatible. Many newer drives
> > don't support this but it looks like the NEC drive mentioned
> > is relatively easy to get.
>
>I suspect that the circuit is nothing more than a way to provide
>enough current to sink the MSX pullups.  Many 3.5" drives are rated
>for 1K pullups and perhaps don't have the current drive capability.
>
>The other explanation is that he wanted to jumper drive select* to
>ready* and had extra gates left over.

Hi Chuck
This may only be an issue for formatting. Normally the drive has
to be spinning for some time to get the controller to lock well
enough to read the headers. The MSX may be different than
the Canon Cat in this respect but since there is only
the one drive, I'd suspect that one might even be able to
just tie off the ready line.
Many machines just do some delay after issuing the motor to
start.
I do like the idea of something that watched the index pulses.
Something with a 555 chip might work or a 123 or like.

>
>A better solution to the ready* problem would be to add a circuit
>that derives it from the index* pulse.
>
>Aren't just about all 1.44MB drives 720K-compatible?  You may have to
>tape over the aperture on a 1.44MB floppy to get it to work, but I've
>yet to see a drive (outside of the NEC 1.3MB 360 RPM 3.5" ones) that
>doesn't speak 720K.

I've been told that there are a few that don't support the 720KB.
I'm not sure what tyhe difference is for the drive. The rpm isn't changed,
just that they use FM instead of MFM. It might be that they change the
size of the read data pulse or something. Pin 2 is a high density select
so it must do something?
Dwight

>
>Cheers,
>Chuck
>

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