18 May
2006
18 May
'06
10:55 a.m.
On May 18 2006, 7:13, dwight elvey wrote:
It definitely doesn't like stepping at around 2 to
2.5 ms someplace.
I send the value 8 to the controller that is suppose to be 4.0 ms and
that works fine.
I don't know how a buffered seek would work on a MFM drive?
Are you saying that it should take in what ever step pulses I send it
and step at 8ms, regardless of what I send.
Not quite, what Chuck means is that most MFM drives after the ST506
have a slightly different interface, and should buffer the step pulses,
and internally it will ramp up the step rate and ramp down again -- it
can step faster once it gets going, than it can if it comes to a stop
between pulses. This style of interface is often called an ST412
interface instead of ST506, because the ST412 was the first drive that
supported it. Below is part of the Seagate data sheet for the ST251.
You'll see the first line identifies it as an ST412-type interface
rather than ST506. You can also see it can accept step pulses at quite
short intervalsi, and should buffer them. If you give it a single
pulse it will take 8ms to move one track, but if you feed it a series
of pulses it should ramp its step rate up (and down when it's close to
the destination cylinder) so that it can step the whole width of the
disk in only 70ms.
ST-251 ST412 MFM
[ connector diagram goes here ]
UNFORMATTED CAPACITY (MB) ________________51.2
FORMATTED CAPACITY (17 SECTORS) (MB) _____42.8
ACTUATOR TYPE ____________________________STEPPER
TRACKS ___________________________________4,920
CYLINDERS ________________________________820
HEADS ____________________________________6
DISCS ____________________________________3
MEDIA TYPE _______________________________THIN FILM
RECORDING METHOD _________________________MFM
TRANSFER RATE (mbits/sec) ________________5.0
SPINDLE SPEED (RPM) ______________________3,600
AVERAGE LATENCY (mSEC) ___________________8.3
INTERFACE ________________________________ST412
SECTORS PER DRIVE ________________________83,640
TPI (TRACKS PER INCH) ____________________777
BPI (BITS PER INCH) ______________________9,935
AVERAGE ACCESS (ms) ______________________40/28*
SINGLE TRACK SEEK (ms) ___________________8
MAX FULL SEEK (ms) _______________________ /70
MTBF (power-on hours) ____________________100,000
POWER REQUIREMENTS: +12V START-UP (amps) _2.0/2.5*
+12V TYPICAL (amps) __0.5
+5V TYPICAL (amps) ___1.0/1.2*
TYPICAL (watts) ______11/12*
MAXIMUM (watts) ______29/36*
BUFFERED STEP PULSE RATE (micro sec) _____3-200
WRITE PRECOMP (cyl) ______________________N/A (821)
REDUCED WRITE CURRENT (cyl) ______________N/A (821)
LANDING ZONE (cyl)________________________AUTO PARK
IBM AT DRIVE TYPE ________________________44, 40, or 3**
--
Pete Peter Turnbull
Network Manager
University of York