33970 datasheet(22/36 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33970

FUNCTIONAL DEVICE OPERATION

LOGIC COMMANDS AND REGISTERS

The bits in Table 18 are read-only bits.

ENB1 (OD15)—This bit indicates if Gauge 1 is enabled.

• 0 = Disabled

• 1 = Enabled

DIR1 (OD14)—This bit indicates the direction Gauge 1

pointer is moving.

• 0 = Toward position 0

• 1 = Away from position 0

DIRC1 (OD13)—This bit determines if the direction of the

most recent pointer movement is toward, or away from, the

last commanded position.

• 0 = Direction of the pointer movement is toward the

commanded position

• 1 = Direction of the pointer movement is away from the

commanded position

CMD1 (OD12)—This bit indicates if Gauge 1 is at the most

recently commanded position.

• 0 = At commanded position

• 1 = Not at commanded position

POS11:POS0 (OD11:OD0)—These 12 bits represent the

actual position of the pointer at the time CS transitions to a

logic [0].

Gauge 0 and 1 Pointer Velocity Status Information

Most recent valid PECCR command resulting in the

Gauge 0 and 1 Pointer Velocity status output:

The bits in Table 19 are read-only bits.

1V7:1V0 (OD15:OD8)—These eight bits represent the

velocity position value (refer to Table 21, page 24) indicating

the actual velocity of Gauge 1 pointer at the time CS

transitions to a logic [0].

0V7:0V0 (OD7:OD0)—These eight bits represent the

velocity position value (refer to Table 21) indicating the

actual velocity of Gauge 0 pointer at the time CS transitions

to a logic [0].

STATE MACHINE OPERATION

The two-phase step motor has maximum allowable

velocities and acceleration and deceleration.The purpose of

the step motor state machine is to drive the motor with

maximum performance while remaining within the motor’s

voltage, velocity, and acceleration constraints.

A requirement of the state machine is to ensure the

deceleration phase begins at the correct time and pointer

position. When commanded, the motor will accelerate

constantly to the maximum velocity, then move toward the

commanded position. Eventually, the pointer will reach the

calculated location where the movement has to decelerate,

slowing safely to a stop at the desired position. During the

deceleration phase, the motor will not exceed the maximum

deceleration.

During normal operation, both step motor rotors are

microstepped with 24 steps per electrical revolution (see

Figure 9). A complete electrical revolution results in two

degrees of pointer movement. There is a second (smaller)

state machine in the IC controlling these microsteps. This

state machine receives clockwise or counter-clockwise index

commands at intervals, stepping the motor in the appropriate

direction by adjusting the current in each coil. Normalized

values are provided in Table 20, page 23.

D11

D10

x = Don’t care.

Table 19. Gauge 0 and 1 Pointer Velocity Status Output Register

Bits

OD15

OD14

OD13

OD12

OD11

OD10

OD9

OD8

OD7

OD6

OD5

OD4

OD3

OD2

OD1

OD0

Read

1V7

1V6

1V5

1V4

1V3

1V2

1V1

1V0

0V7

0V6

0V5

0V4

0V3

0V2

0V1

0V0

Write

–

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