PC33991DHSLASHR2 datasheet(17/36 Pages) MOTOROLA

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MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

33991

RZ12–RZ5—These bits must be transmitted as logic [0] for

valid commands.

RZ4—This bit is used to enable an unconditional RTZ event.

• 0 = Automatic return to zero

• 1 = Unconditional return to zero

RZ3–RZ2—These bits are used to determine which eight

bits of the RTZ accumulator will be clocked out via the SO

pin. See Table 8.

RZ1–Return to zero—Commands the selected gauge to

return the pointer to zero position.

• 1 = Return to zero enabled

• 0 = Return to zero disabled

RZ0–Gauge Select: Gauge 0/Gauge 1—Selects the gauge

to be commanded.

• 0 = Selects Gauge 0

• 1 = Selects Gauge 1

Gauge Return to Zero Configuration Register

SI Address 101–Gauge Return to Zero Configuration

Table 9. It is written to modify the step time, or rate, the pointer

moves during an RTZ event. Also, the integration blanking time

is adjustable with this command. Integration blanking time is the

time immediately following the transition of a coil from a driven

state to an open state in the RTZ mode. Finally, this command

is used to adjust the threshold of the RTZ integration register.

The values used for this register are chosen during

development to optimize the RTZ for each application. Various

resonance frequencies can occur due to the interaction

between the motor and the pointer. This command permits

moving the RTZ pointer speed away from these frequencies.

Bits D3:D0 determine the time spent at each full step during

an RTZ event. The step time associated with each bit

combination is illustrated in Table 10. The default full step time

is 21.25 ms (0101). If there are 2 full steps per degree of pointer

movement, the pointer speed is: 1/(FS

×2) degrees.

Bit D4 determines the provided blanking time immediately

following a full step change, and before enabling the integration

of the non-driven coil signal. The blanking time is either 512 µs,

when D4 is logic [0], or 768 µs when D4 is logic [1].

Detecting pointer movement is accomplished by integrating

the back EMF present in the non-driven coil during the RTZ

event. The integration circuitry is implemented using a Sigma-

Delta converter resulting in a representative value in the 15-bit

RTZ accumulator at the end of each full step. The value in the

RTZ accumulator represents the change in flux and is

compared to a threshold. Values above the threshold indicate a

moving pointer. Values below the threshold indicate a stalled

pointer, thereby resulting in the cessation of the RTZ event.

The RTZ accumulator bits are signed and represented in

two’s complement. If the RTZR D3:D2 bits were written as 10 or

11, the ST14 bit corresponds to bit D14 of the RTZ accumulator,

the sign bit. After a full step of integration, a sign bit of 0 is the

indicator of an accumulator exceeding the decision threshold of

0, and the pointer is assumed to still be moving. Similarly, if the

sign bit is logic [1] after a full step of integration, the accumulator

value is negative and the pointer is assumed to be stopped. The

integrator and accumulator are initialized after each full step.

Accurate pointer stall detection depends on a correctly

preloaded accumulator for specific gauge, pointer, and full step

combinations. Bits D12:D5 are used to offset the initial RTZ

accumulator value, properly detecting a stalled motor. The

initial accumulator value at the start of a full step of integration

is negative. If the accumulator was correctly preloaded, a free

moving pointer will result in a positive value at the end of the

integration time. A stalled pointer results in a negative value.

The preloaded values associated with each combination of bits

D12:D5 are illustrated in Table 11. The accumulator should be

loaded with a negative value resulting in a transition of the

accumulator MSB to a logic [1] when the motor is stalled. After

a power-up, or any reset in the Default mode, the 33991device

sets the accumulator value to -1, resulting in an unconditional

RTZ pointer movement.

These bits are write-only.

RC12–RC5—These bits (D12:D5) determine the preloaded

value into the RTZ integration accumulator to adjust the

detection threshold. Values range from -1 (00000000) to -4081

(11111111)provided in Table 11.

RC4—This bit determines the RTZ blanking time

•0 = 512 µs

•1 = 768 µs

RC3–RC0—These bits (D3:D0) determine the full step time

during an RTZ event, determining the pointer moving rate. Step

times range from 4.86 ms (0000) to 62.21 ms (1111). Those are

illustrated in Table 10. The default time is 21.25 ms (0101).

Table 8. RTZ Accumulator Bit Select

RTZ Accumulator Bits to SO Bits

ST15:ST8

[7:0]

[11:4]

[14:8]

Table 9. RTZCR SI Register Assignment

Address 101

D12

D11

D10

Write

RC12

RC11

RC10

RC9

RC8

RC7

RC6

RC5

RC4

RC3

RC2

RC1

RC0

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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