Step; Buffered Seek; Figure Il Read/Write Timing - Seagate ST212 Product Manual

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STEP
FIGURE 11:
ReadlWrite Timing
The STEP signal is a 2 p,sec. minimum width pulse that initiates Read/Write
head motion. The number of pulses issued determines distance traveled. The
rate of Step pulses determines the access method.
If the period between pulses is from 5 p,sec. to 500 p,sec., the access method will
be Buffered-Seek. Slow-Step is employed if the period between pulses is greater
than or equal to 3 msec.
DIRECTION IN must be stable 100 nsec. before the leading edge of the first
step pulse and remain stable for 100 nsec. after the last pulse in a string of Step
p.ulses. Step pulses issued between 500 p,sec. and 3 msec. may be lost.
If excessive Step pulses are issued which would cause a seek inward beyond
cylinder 306 or outward beyond Cylinder Zero, the drive will enter the Auto-
'll:uncation mode. Refer to Section 4.3.4.
4.3.1 BUFFERED SEEK
Th minimize access time, pulses may be issued
at
an accelerated rate and buffered
in
a counter. Initiation of a seek starts immediately after the frrst pulse is received.
Head motion occurs during pulse accumulation, and the seek is completed fol-
lowing receipt of all pulses.
14
ST212 PRODUCT MANUALIRev. B