3 Mar
2011
3 Mar
'11
12:22 p.m.
On 3 Mar 2011 at 10:58, Chris Elmquist wrote:
What is the theory of operation behind a hard-sector
filter? I
believe I have seen this done with just a one-shot but I'm not sure I
understand how that eliminates only the sector marks, leaving just
index? It seems like with just a one-shot, it would sync to any hole
and call that index.
One of the things that makes this easy for 8" drives is that, but for
a few very early types, all 8" HS floppies are 33-hole (32 sectors +
index).
The index on an 8" HS floppy is located midway between two sector
holes. So, for example, if you use a one-shot whose output width is
set to, say, 2/3rds of the time between index holes, any hole
occurring under that "umbrella" must be an index--so you generate an
"index" pulse. Very simple, actually.
--Chuck