Theory Of Operation; Functional Description; Drive Select; Power-Up Mode - Siemens Microfloppy FDD100-5 Operating And Maintenance Manual

SECTION 4
THEORY OF OPERATION
4.1 FUNCTIONAL DESCRIPTION
Figure 4-1 is a functional block diagram that shows overall operation of the Model FDD1 00-5 Disk
Drive. The disk drive has one main PWB which contains Read, Write, and Control logic, and a small
servo control PWB which contains the speed-control circuit for the spindle drive motor.
4.1.1 DRIVE SELECT
Disk drive selection occurs when the Drive Select line that corresponds to a particular disk drive
is active. Only the disk drive in which this line is active will respond to input lines. Under normal
operation, the Drive Select line will load the read/write (R/W) head, enable the input lines, and
activate the output lines. Optional modes of operation are available to the user.
4.1.2 POWE R-UP MODE
The two DC power sources can be applied to the disk drive in any sequence; however, once power
has been applied, a 1-second delay must be allowed before any Read or Write operation is at-
tempted. This delay is for stabilization of the diskette rotational speed and must be allowed any-
time the Motor On line is activated. When DC power is applied, a Power On Reset (POR) pulse
automatically resets the electronics and inhibits inadvertent writing or erasing on the diskette.
Therefore, the disk drive is ready for operation after application of DC power and one second after
activation of Motor On; also, the initial position of the R/W head with respect to data tracks is
indeterminate immediately after application of DC power. To ensure proper positioning of the
R/W heads before any Read or Write operation, a Step Out operation for each disk drive should
be performed until the Track
00
status signal becomes active.
4.1.3 HEAD LOAD SIGNAL LINE (OPTION)
The Head Load signal is applied through control logic to the Head Load solenoid. The solenoid
allows the diskette envelope with its rotating media to be pushed against the R/W head so that
contact is made through the slot in the envelope. The Head Load signal line is optional. Without the
use of this option, the head is loaded when either the Drive Select or Motor On signals are activated.
4-1