10 Apr
2000
10 Apr
'00
6:39 p.m.
ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
Hi
The circuit is clever. The output of the '121 goes to
the data pin of a '74. Both the '121 and '74 are clocked
by the index pulse. If it is the index and not the
sector pulse, the output signal of the '121 gets clocked
through the '74. If it is just another sector pulse,
the '121 has timed out and the output of the '74 doesn't
change.
I was looking at the Athana site. Has anyone dealt with
them? How much do they charge for a box of 10 8-inch disk?
Is anyone planning on making a purchase soon, they have
a $100 minimum?
Dwight
two sector holes. It uses a 74121 one shot to
detect
this signal. The resistor and capacitor give the following
timing: 0.7 ( 0.22e-6 * 22e3 ) = 3.4 ms. I would think
that this signal would be about 3/4 of a sector to
catch the index mark in the middle. As I recall,
Yes, that sounds reasonable. The monostable triggers on each sector hole,
but as it's non-retriggerable, it can't retrigger on the index hole (well,
not after the first revolution, possibly). And 3/4 of the sector time
would be a reasonable value to aim at.