26 Dec
2006
26 Dec
'06
12:56 p.m.
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