Seagate ST212 - 4.3.3 Auto-Truncation; 4.4 Direction In

4.3.3
AUTO.:rRUNCATION
The drive will enter the Auto-Truncation mode if the controller issues an exces-
sive number· of Step pulses, which would place the Read/Write heads outward
beyond Track
0 or inward beyond cylinder 306.
With the Auto-Truncation mode active, the drive disallows additional pulses, takes
control
of the stepper motor and recalibrates the heads to Track 0.
CAUTION: If the controller is still issuing Slow-Step pulses after the drive is-
sues SEEK COMPLETE from Auto-Truncation mode, the
ST212 will either
reenter Auto-Truncation mode with DIRECTION IN false,
or step the remain-
ing cylinders with DIRECTION
IN true.
I-EXCESSIVE STEP PULSES RECOGNIZED
-TRACKJj 1
--- .. ,,---- .. /jt--------
- SEEK 1 20msec max.-1 1-
1+1------ 2sec max.------~.I
FIGURE 14:
Auto-truncation Timing
4.4
DIRECTION IN
DIRECTION IN defines the direction the Read/Write heads will move when
the. STEP line is pulsed. With DIRECTIONIN true, each pulse causes the heads
to move one cylinder inward toward the spindle. With DIRECTION IN false,
each pulse causes the heads to move one cylinder outward toward Track 0.
4.5
DRIVE SELECT
The DRIVE SELECT line is activated by the controller to select and address
the drive. Refer to
Section 3.0.
16
ST212 PRODUCT MANUAL/Rev. B