SLFS040

– DECEMBER 1993

POST OFFICE BOX 655303

DALLAS, TEXAS 75265

23

PRINCIPLES OF OPERATION

Table 6. Port-C Definition (System Control Functions)

BIT #

NAME

SUBSYSTEM

DESCRIPTION

0

SPNENA

SPN

Spindle power-inverter enable

1

START

SPN

Spindle-operation mode

2

NHALLS

SPN

No Hall-commutation-mode select

3

UPOLAR

SPN

Spindle-inverter unipolar select

4

COMM

SPN

Spindle-inverter advance (no hall mode)

5

SPNMODE

SPN

Select DAC current-control mode

6

VCMENA

VCM

VCM power output enable

7

BRAKE

SPN

Spindle BRAKE enable

8

BEMF GAIN

SPN

Back-EMF amplifier sense gain

9

AUX0

SYS

AUXOUT function select MSB

10

AUX1

SYS

AUXOUT function select LSB

11

AWAKE

SYS

System power enable

12

PT0

SYS

Port-select LSB

13

PT1

SYS

Port-select MSB

14

ID0

SYS

Device-select LSB

15

ID1

SYS

Device-select MSB

Port-C system control bit definitions

AWAKE

This bit controls the dc bias conditions in the device. When this bit is low, the device is in the sleep mode and

all dc bias sources, with the exception of the voltage monitor, are disabled. All logic, with the exception of the

serial register, is disabled, and device power dissipation is minimized. When this bit is high, the device is awake

and power dissipation is maximum.

AUX1

AUX1 is the MSB of the auxiliary logic control functions (see Table 7).

AUX0

AUX0 is the LSB of the auxiliary logic control functions (see Table 7).

BEMF GAIN

This bit controls the gain of the back-EMF sense amplifier. When the bit is low, the forward back-EMF gain sense

(measured at Vphase) is one. When the bit is high, the forward sense gain is five. This function is intended to

start the spindle motor in back-EMF mode.

BRAKE

BRAKE enables the high-side power inverters and disables the low-side power drivers. The brake is normally

implemented after a retract has occurred and the head has reached the head stop.

VCMENA

VCMENA enables the VCM output drivers. In the disabled state, the VCM output power amplifier outputs go low.

However, the power amplifiers still have dc bias applied and can be enabled in a short period of time.