PXD10RM Datasheet, PDF (216/1332 Pages) Freescale Semiconductor, Inc – PXD10 Microcontroller

This feature can be enabled by programming the en_pll_sw bit in CR. Then, when the input pin pll_select
goes high, the output clock ck_pll_div will progressively increase its frequency as described in Table 8-30
and Figure 8-22.
Table 8-30. Progressive clock switching on pll_select rising edge
Number of PLL output clock cycles
ck_pll_frequency (PLL output clock frequency)
8
16
32
onward
(ck_pll_out frequency)/8
(ck_pll_out frequency)/4
(ck_pll_out frequency)/2
(ck_pll_out frequency)
ck_pll_out
8
4
ck_pll_div
2
1
Figure 8-22. Diagram of progressive clock switching
8.9.6.3 Normal Mode with frequency modulation
The FMPLL default mode is without frequency modulation enabled. When frequency modulation is
enabled, however, two parameters must be set to generate the desired level of modulation: the PERIOD,
and the STEP. The modulation waveform is always a triangle wave and its shape is not programmable.
FM modulation shall be activated in two steps:
• first: configure the FM modulation characteristics : MOD_PERIOD, INC_STEP.
• second: enable the FM modulation by programming the FM_EN bit of MR register to 1. FM
modulated mode can be enabled only when PLL is in lock state.
To latch these values inside the PLL, two ways are usable depending on the value of STRB_BYPASS
register bit in MR.
If STRB_BYPASS is low, the modulation [parameters are latched in the PLL only when the STRB signal
goes high for at least 2 cycles of INFIN clock. The STRB signal is automatically generated in the PLLD
when the modulation is enabled (FM_EN goes high) if the PLL is[ locked (s_lock=1) or when the
modulation has been enabled (FM_EN=1) and PLL enters in lock state (s_lock goes high).
If STRB_BYPASS is high, the STRB signal is bypassed. In this case, control bits (MOD_PERIOD[12:0],
INC_STEP[14:0], SPREAD_CONTROL) need to be static or hardwired to constant values. The control
bits must be changed only when the PLL is in power down mode.
The modulation depth in % is
8-38
PXD10 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
Freescale Semiconductor