Table of Contents
Advertisement
Theory of Operation 2·5
Seek Operation
Before reading or writing a sector of data, the controller must position the read/write head
of the disc drive over the desired sector. To do this, the controller sends signals to the disc
drive to step the head to the desired track. The controller then begins to read the disc. Track
and sector information is stored as a preamble to each sector, and the disc is formatted in a
manner to allow the controller to detect the beginning of a preamble. On finding a pream-
ble, the Z80A first checks that the track number is correct.
[f
not, it will continue to step the
head until the correct track is found. The sector number is then compared. [f correct, the
Z80A waits for the mark to indicate the beginning of the data field and then begin reading or
writing the data field. lf incorrect, it passes over this sector and looks for the next until
it
finds
the desired sector.
[f
it can't find the sector after two revolutions of the disc, an error
condition is indicated to the host system.
Drive Theory of Operation
Introduction
This section provides a general description of the drive module, part number 09895-69430.
Since this module is still being modified, this description will only cover those areas common
to all versions.
General Description
The basic function of the drive is to indicate to the controller when it is ready to operate, and
respond to the commands of the controller to:
•Receive and generate control signals,
•Position the read/write heads to selected tracks,
•Read or write data on the disc when selected.
Signals received and transmitted by the drive are shown in Table 2-1. Some signals received
by the drive are gated with drive select so that no stepping, reading or writing can be
performed on an unselected drive. Also, some signals generated within the drive are gated
with drive select so that they can't be transmitted from an unselected drive.
Advertisement
Table of Contents
