FXTH87xx11 and FXTH87xx12 Embedded Firmware User Guide, Rev. 2.1
6
Freescale Semiconductor, Inc.
Globals and formats
2.3
Universal Uncompensated Measurement Array (UUMA) format
The FXTH87xx11 and FXTH87xx12’s measurement routines are divided into two subsets: routines that
return uncompensated measurements, and routines that take uncompensated measurements as arguments
and return compensated measurements.
In order to be consistent and keep the number of CPU cycles down, all uncompensated measurement
routines will return data following the array format described in
, and all compensating routines
will take data from the same array.
This array is referred to as Universal Uncompensated Measurement Array (UUMA). It can be located
anywhere the user decides.
Each element must be 16-bits long (two bytes) regardless of what the actual bit-width of the measurement
is.
Each individual uncompensated measurement routine will only update its corresponding item. For
example, calling the TPMS_READ_VOLTAGE routine will only modify the voltage element of the array.
The rest will remain unchanged.
Compensation routines do not modify any elements in the UUMA.
2.4
Simulated SPI interface Signal Format
The FXTH87xx11 and FXTH87xx12 include three routines (TPMS_MSG_INIT, TPMS_MSG_READ
and TPMS_MSG_WRITE) that, when used together, allow the user to perform serial communication with
the device through a simulated SPI interface.
The following assumptions are made:
•
Only two pins are used: PTA0 for data (both incoming and outgoing) and PTA1 for clock. No slave
select is included by default, but the user may use any other pin if required.
•
The data pin has a pull-up resistor enabled.
•
The FXTH87xx11 and FXTH87xx12 will be a master device (the FXTH87xx11 and FXTH87xx12
will provide the clock).
•
Data can be read/written 8-bits at a time.
•
Speed of the interface is dependant on bus clock settings.
•
Data is transferred MSB first.
Table 4. Universal Uncompensated Measurement Array
Index
Content
0
Uncompensated Voltage
1
Uncompensated Temperature
2
Uncompensated Pressure
3
Uncompensated X-Axis Acceleration
4
Uncompensated Z-Axis Acceleration
