NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
• A successive approximation algorithm is used to calculate the optimum sub-band.
• Fc, the Center Frequency (AFREQ+BFREQ)/2 is used as the reference frequency for
the VCO calibration in FSK mode (MOD = 1).
• BFREQ is used as the reference frequency for the VCO calibration in OOK mode
(MOD = 0).
• Calibration occurs every time the VCO is enabled.
• The calibration takes approximately 5 μs.
The state machine of the calibration is shown in Figure 47.
· Maxband is the number
VCOband = maxband/2
of sub-band of the VCO
Bestband = maxband/2
· Bestband is the band which
Difference = maxband/4
is going to be chosen
· Difference is an internal variable.
Count the number of
cycles of the VCO
Compare
VCOcount and Targetedcount
Difference = Difference/2
VCOcount > Targetedcount
VCOcount < Targetedcount
VCOcount = Targetedcount
no
VCOband = VCOband + Difference
VCOband = VCOband - Difference
Bestband = VCOband
VCOband = VCOband - Difference
Difference = 1?
Bestband is first best band found
or the closest band found
yes
aaa-028040
Figure 47.ꢀVCO calibration state machine
16 Firmware
This section describes the software subroutines contained in the firmware section of
the FLASH memory that the user can call for various tasks and to reduce the software
development time for the main internal operations.
16.1 Software jump table
All subroutines are accessed through a jump table located at the bottom of the firmware
FLASH memory as described in Table 161. This allows upgrades in firmware without
changing the software code of the user. All subroutines should be accessed with the JSR
instruction.
16.2 Function documentation
The following subsections describe the details of the firmware routines. Further details
can be found in the latest version of the FXTH87E Embedded Firmware User Guide.
FXTH87ERM
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© NXP B.V. 2019. All rights reserved.
Reference manual
Rev. 5.0 — 4 February 2019
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