Fujitsu MAF3364FC SERIES Maintenance Manual page 43

The DSP accurately controls traffic positioning of each head using servo information on the data
surface.
(3) Spindle motor drive circuit
The spindle motor drive circuit drives the spindle motor. A drive current in the motor coil
generates a counter emf. The frequency of the counter emf is compared, by the DSP, with a
reference frequency derived by dividing the crystal oscillator frequency. The DSP uses the result
of the comparison to control the rotational frequency of the spindle motor.
(4) Controller circuit
The controller circuit has the following main functions:
Fibre channel control
Data buffering (4 MB, 1 to 32 segments)
SCSI protocol control and data transfer control
Sector format control
ECC
Error recovery and self-diagnosis
5 - 4 C141-F037-02EN