19 Apr
2009
19 Apr
'09
3:17 p.m.
On 19 Apr 2009 at 20:13, Philip Pemberton wrote:
- If you add something to sync to the index marks
and generate a
hard-sector "emulation" index pattern from that, you can't put a HS
disc in that drive
Not so--it'd work the same way my PIC solution does--while it's
sampling the drive speed (and not passing index pulses) it's looking
for sector holes. If it finds them, it hangs back and allows index
pulses to flow through. If it sees an index pulse every 166/200 msec
or so, it knows to start generating sector pulses on the next rev.
What about just detecting the speed of the input index
pulse? If
they're turning up faster than, say, once every quarter-second, then
bypass the index-pulse multiplier. Basically have a multiplexer that
allows the output to be sourced from /Index_In, or /Index_Generated.
Exactly what my PIC code does. But the base issue is really the ISV
characteristics of the drive's speed control. Direct-drive 3.5"
drives are probably much better than old 5.25" belt-drive drives. I
suspect that consistent speed control issues may have originally
been the reason for NEC specifying 8x512 format for a "360K"
diskette.
--Chuck