33813 Datasheet, PDF (31/54 Pages) Freescale Semiconductor, Inc – One Cylinder Small Engine Control IC

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.
Table 12. SPI VRS Manual Configuration Register
SPI VRS Configuration/Control Register
Bits 3,2,1,0
0000 (default)
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Blanking Time in%
(of last pulse high period)
0.0
3.12
6.25
9.37
12.5
15.62
18.75
21.87
25
28.1
31.3
34.4
37.5
40.6
43.8
46.9
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.
Analog Integrated Circuit Device Data
Freescale Semiconductor
33813
31