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MPC563XM Reference Manual, Rev. 1
574
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
17.5.5
Frequency Modulation
Frequency modulation uses a triangular profile as shown in
. The modulation frequency and
depth are set using the MODPERIOD and INCSTEP fields of the SYNFMMR register.
Figure 17-8. Triangular Frequency Modulation
The following equations define how to calculate MODPERIOD and INCSTEP based on the frequency of
the feedback divider (f
ref
), the modulation frequency (f
mod
) and the modulation depth percentage (MD):
Table 17-14. Loss-of-Clock Interrupt Request
Operating Mode
LOCEN
1
1
LOCEN is the loss-of-clock enable bit in either SYNCR or ESYNCR2, depending on the ESYNCR1[EMODE] bit.
LOCIRQ
2
2
LOCIRQ is the loss-of-clock interrupt enable bit in either SYNCR or ESYNCR2, depending on the ESYNCR1[EMODE] bit.
Interrupt Request
Reference Failure
FMPLL Failure
Bypass mode with external reference and PLL off
—
—
—
—
Bypass mode with crystal reference and PLL off
—
—
No
—
Bypass mode with external reference and PLL running
—
—
—
—
Bypass mode with crystal reference and PLL running
—
—
No
—
Normal mode with external reference
0
—
—
No
1
0
—
No
1
1
—
Yes
Normal mode with crystal reference
0
—
No
No
1
0
No
No
1
1
Yes
Yes
2 x MD
MD
f
sys
f
sys
Center Spread
Down Spread
f
sys
= PLL nominal frequency
MD = Modulation depth percentage
MODPERIOD
round
f
ref
4
f
mod
×
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)
=