33813 datasheet(31/54 Pages) FREESCALE

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Analog Integrated Circuit Device Data



Freescale Semiconductor

33813

5.1.27 Input Comparator Threshold Values

The threshold voltage for the input comparator is produced by a 4-bit D/A converter. The control of the D/A output value is by

means of the upper four bits of the SPI VRS configuration register or the upper four bits of the SPI VRS control register. When

the contents of the SPI VRS control register contains all zeros, the binary value for the D/A threshold is taken from the value in

the SPI VRS configuration register. When the contents of the SPI VRS control register is non-zero, then the value in the upper

four bits of the SPI VRS control register is used to set the D/A output. The values outputted by this D/A, using either the SPI VRS

control register or the SPI VRS Configuration register, are listed in Table 11 in the threshold values table. The blanking one-shot

time is also set via the lower 4 bits of the SPI VRS configuration register or the SPI VRS control register using the same condition,

as described previously for the threshold D/A.

5.1.28 Blanking Time Definitions

The values for the one shot blanking, as a percentage of the last high output pulse period is shown in Table 12.

5.1.29 Manual and Automatic Modes

The SPI VRS miscellaneous configuration register has a bit to enable the automatic selection of the comparator threshold (bit 7).

At this time, the operation of automatic mode remains TBD.

5.1.30 VRS Peak Detector

The VRS peak detector determines the magnitude of the positive peak of the VRS input signal and digitizes it. The value of the

VRS peak voltage is reported in the VRS SPI status register bits 7, 6, 5, and 4. The MCU can read the value of peak voltage after

the zero crossing time of the input pulse, and uses this information to set the threshold and blanking parameters for subsequent

input pulses. Status bits reflect the last detected peak and only read 0000 after a POR or SPI reset command.

Table 12. SPI VRS Manual Configuration Register

SPI VRS Configuration/Control Register

Bits 3,2,1,0

Blanking Time in%

(of last pulse high period)

0000 (default)

0.0

0001

3.12

0010

6.25

0011

9.37

0100

12.5

0101

15.62

0110

18.75

0111

21.87

1000

1001

28.1

1010

31.3

1011

34.4

1100

37.5

1101

40.6

1110

43.8

1111

46.9

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