NEC FD1165 - Head Load (HDL); Step (STP); Direction Select (DIR); Side Select (SSL)

3.3.2 Head Load (HDL)
When the disk drive is in the ready state, a Low on this
line initiates loading of the read/write heads.
3.3.3 Step (STP)
This pulse directs the stepping motor to move the read/write
heads from track to track. The direction of movement is
determined by the Direction Select signal (see Section
3.3.4). Figure 3-3 shows the repetition rate and width of
the Step pulse. The heads start to move at the leading
(positive-going) edge of each pulse. One pulse moves the
heads 1/2 track.
STP-----U u
-1W~T-1
u
T =3 ms (MIN)
W = 1 J1S TO 2.5 ms
Figure 3-3 Step Signal Timing
3.3.4 Direction Select (DIR)
If the Direction Select signal is High, the head moves
toward the external tracks. If DIR is Low, the head moves
toward the internal tracks. The trailing edge of this sig-
nal occurs 1 ~s before the leading edge of the STP signal.
3.3.5 Side Select (SSL)
This signal selects the side of the disk that is used for
the read/write operation. If the Side Select signal is
High, side 0 (upper side) is selected. If SSL is Low, side
1 (lower side) is selected. When a single-sided flexible
disk is used, side 0 is selected. The SSL signal must occur
at least 100 ~s before the read/write operation begins.
3-4