3.2.2 Control Circuits
Refer to Figure 3·6.
All control circuits are mounted on the main circuit card assembly and are
primarily on the Control IC (one chip).
The control circuits receive data from the various sensors and circuits and provide
output signals to the Read/Write IC and the interface.
Detectors· All detectors (photo-transistors) are mounted on either the write
protect circuit card, disk-in senSor assembly, or track 00 sensor assembly.
The individual detectors are described in paragraph 3.1.
Drive Select and Indicator Gate Circuits - These circuits determine the
drive's select status and also when the Front Bezel indicator will be lit.
These circuits operate in conjunction with the position of the Drive Select
Jumper (Position 0 through
3 which are set by the user) and the
corresponding Drive Select interface signal.
Head Load Gate - This circuit, in conjunction with selection jumpers,
determines the set of conditions that must be present to cause the
Read/Write heads to load.
Write/Erase Gate Circuits - These circuits determine when current will flow
through the Write and Erase coils (in the selected Read/Write Head) for
recording on the disk. . These circuits operate in conjunction with the Write
Gate interface signal. Erase current is delayed (the required period of time)
to correspond to the beginning and ending of write current.
Spindle Motor Gate - This output circuit determines the speed of the spindle
Ready Detect Circuits - This circuit receives Index .pulses (from the Index
Detector) and sets the Ready signal true when the disk reaches its correct
Stepping Motor Control Circuits - These circuits, in conjunction with the
over-drive single shot circuit and the Direction and Step interface signals,
determine the movement of the Stepping Motor.
The timing chart in Figure 3-7 shows typical stepping motor control
The output of the Step pulse generator circuit turnQ on the over-
drive circuit for the prescribed time (approximately 30 milliseconds).
During this time +12V is activated on the stepping motor coil and a
high level of torque is available for seeking and centering the head
After centering is completed, +5V is applied to the
stepping motor coil for holding the head carriage at the correct
position (and to lower power requirements and excessive heating of
the motor coil).