Chapter 4 Clock Description
MPC5602P Microcontroller Reference Manual, Rev. 4
94
Freescale Semiconductor
Figure 4-9. Progressive clock switching scheme
4.8.6.3
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.
Frequency modulation is activated as follows:
1. Configure the FM modulation characteristics: MOD_PERIOD, INC_STEP.
2. Enable the FM modulation by programming bit SSCG_EN of the MR to ‘1’. FM modulated mode
can be enabled only when PLL is in lock state.
There are two ways to latch these values inside the FMPLL, depending on the value of bit STRB_BYPASS
in the MR.
If STRB_BYPASS is low, the modulation parameters are latched in the PLL only when the strobe signal
goes high. The strobe signal is automatically generated in the FMPLL when the modulation is enabled
(SSCG_EN goes high) if the PLL is locked (s_lock = 1) or when the modulation has been enabled
(SSCG_EN = 1) and PLL enters in lock state (s_lock goes high).
If STRB_BYPASS is high, the strobe signal is bypassed. In this case, control bits (MOD_PERIOD[12:0],
INC_STEP[14:0], SPREAD_CONTROL) must be changed only when the PLL is in power down mode.
The modulation depth in % is
Eqn. 4-2
NOTE
The user must ensure that the product of INCSTEP and MODPERIOD is
less than (2
15
– 1).
The following values show the input setting for one possible configuration of the PLL:
•
PLL input frequency: 4 MHz
•
Loop divider (LDF): 64
•
Input divider (IDF): 1
•
VCO frequency = 4 MHz × 64 = 256 MHz
onward
(ck_pll_out frequency)
Table 4-8. Progressive clock switching on pll_select rising edge (continued)
Number of PLL output clock cycles
ck_pll_div frequency (PLL output frequency)
Division factors
ck_pll_out
ck_pll_div
of 8, 4, 2, or 1
ModulationDepth
100 5
INCSTEPxMODPERIOD
2
15
1
–
MDF
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