Frequency Modulated Phase-Locked Loop (FMPLL)
Freescale Semiconductor
6-21
PXR40 Microcontroller Reference Manual, Rev. 1
2. Write the SYNFMCR[FMDAC_EN] bit to logical 1 (to enable FMDAC_CTL) and the
SYNFMCR[FMDAC_CTL] bit field to the appropriate value shown in
.
3. Program the desired modulation rate into the ERATE field of the ESYNCR2 register and set the
EDEPTH field to a non-zero value. The absolute value in the EDEPTH field is non-critical as this
value is not used for actual FM depth, however EDEPTH must be non-zero to enable FM. Make
sure not to change ERFD from step 2 when setting ERATE and EDEPTH as they share the same
register space.
4. Wait for the PLL to lock. When the PLL achieves lock, write the desired ERFD value. Make sure
not to modify ERATE/EDEPTH as they share the same register space.
The frequency modulation system is dependent on several factors, including the accuracies of the
V
DDSYN
/V
SSSYN
voltage, of the crystal oscillator frequency, and of the manufacturing variation.
For example, if a 5% accurate supply voltage is used, then a 5% modulation depth error results. If the
crystal oscillator frequency is skewed from the nominal operating frequency, the resulting modulation
frequency is proportionally skewed. Finally, the error due to the manufacturing and environment variation
alone can cause the frequency modulation depth error to be greater than 20%.
Table 6-12. FMDAC_CTL settings for FM Configuration
Peak-to-Peak FM depth
(EDEPTH)
FMDAC_CTL
1% (center frequency ±0.5%)
0x04
2% (center frequency ±1.0%)
0x08
3% (center frequency ±1.5%)
0x0C
4% (center frequency ±2.0%)
0x10
Summary of Contents for PXR4030
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