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

Chuck Guzis cclist at sydex.com
Tue Dec 26 14:56:28 CST 2006


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.

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.

Cheers,
Chuck




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