Frequency Modulated Phase Locked Loop and System Clocks (FMPLL)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
Freescale Semiconductor
11-29
Figure 11-10. Frequency Modulation Waveform
11.4.3.3
FM Calibration Routine
Upon enabling frequency modulation, a new calibration routine is performed. This routine tunes a
reference current into the modulation D/A so that the modulation depth (F
max
and F
min
) remains within
specification.
Entering the FM calibration mode requires the user to program SYNCR[EXP]. The EXP is the expected
value of the difference between the reference and feedback counters used in the calibration of the FM
equation:
For example, if 80 MHz is the desired final frequency and an 8 MHz crystal is used, the final values of
MFD = 6 and RFD = 0 produces the desired 80 MHz. For a desired frequency modulation with a 1% depth,
then EXP is calculated using P = 1, MFD = 6 and M = 480. Refer to
for a complete list of
values to be used for the variable (M) based on MFD setting. To obtain a percent modulation (P) of 1%,
the EXP field would have to be set at:
F
max
= F
sys
+ {1%, 2%}
F
min
= F
sys
– {1%, 2%}
F
mod
= F
ref_crystal
or F
ref_ext
/
( 1) Q where Q = 40 or 80
F
max
Δ
Fm
t
F
min
f
Δ
t =
1
F
mod
Δ
Fm
EXP
MFD
4
+
(
)
M
×
P
×
(
)
100
------------------------------------------------------
=
EXP
6
4
+
(
)
640
×
1
×
(
)
100
÷
48
=
=
Содержание MPC5565
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