NXP Semiconductors
UM11227
NTM88 family of tire pressure monitor sensors
UM11227 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2020. All rights reserved.
User manual Rev. 6 — 24 April 2020
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4.4 Definition of signal ranges
Each measured parameter (pressure, voltage, temperature, acceleration) results from
an ADC10 conversion of an analog signal. This ADC10 result may then be passed
by the firmware to the application software as either the raw ADC10 result or further
compensated and scaled for an output between one and the maximum digital value
minus one. The minimum digital value of zero and the maximum digital value are
reserved as error codes.
The signal ranges and their significant data points are shown in Figure 1. In this
definition, the signal source would normally output a signal between S
INLO
and S
INHI
. Due
to process, temperature, and voltage variations, this signal may increase its range to
S
INMIN
to S
INMAX
. In the example case of 10-bit raw conversions and 9-bit compensation,
the signal is between the supply rails, so that the ADC10 converts it to a range of digital
numbers between 0 and 1023. These digital numbers have corresponding D
INMIN
, D
INLO
,
D
INHI
, D
INMAX
values. The ADC10 digital value is taken by the firmware and compensated
and scaled to give the required output code range.
SENSOR
ANALOG
VOLTAGE
ADC10 RAW
DIGITAL
(10-BIT CONVERSION)
CALCULATED
DIGITAL
(9-BIT EXAMPLE)
SIGNAL
SOURCE
ADC10
FIRMWARE
ROUTINE
511
510
0
1
256
0
1023
512
VDD/2
VDD
VDD
SINMAX
SINHI
SINMIN
SINLO
DINMAX
DINHI
DINLO
DINMIN
NORMAL CASE
UNDERFLOW
LOWER ERROR CASE
CASE
OVERFLOW
CASE
FORCE
OUTPUT
TO 511
FORCE
OUTPUT
TO ZERO
UPPER ERROR CASE
aaa-028041
Figure 1. Measurement signal range definitions
Digital input values below D
INMIN
and above D
INMAX
are immediately flagged as being out
of range and generate error bits and the output is forced to the 0 value.
Digital values below D
INLO
(but above D
INMIN
) or above D
INHI
(but not D
INMAX
) will most
likely cause an output that would be less than 1 or greater than 510, respectively. These
cases are considered underflow or overflow, respectively. Underflow results will be forced
to a value of 1. Overflow results will be forced to a value of 510.
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