Freescale Semiconductor MPC5604B, Quick Start Manual

Page: 19 / 150

Figure 19 : FMPLL Modulation Register (Reference Manual Rev8 – Fig. 6-8)
Different fields of this register are defined as:

STRB_BYPASS: Strobe bypass; when this bit is set to ‘0’, it allows to change other fields
while FM is not enabled, but if it is set to ‘1’, other fields has to be static while FMPLL is
powered on,

SPRD_SEL: spread selection, if it is ‘0’, the FM is centre spread, if it is ‘1’, the FM is down
spread (see Figure 18),

MOD_PERIOD[12:0]: binary value of
𝑓
𝑟𝑒𝑓
4𝑓
𝑚𝑜𝑑
, where 𝑓
𝑟𝑒𝑓
= 𝑃𝐻𝐼 .
𝑂𝐷𝐹
𝑁𝐷𝐼𝑉
and 𝑓
𝑚𝑜𝑑
is the
modulation frequency,

INC_STEP[14:0]: binary value of 𝑖𝑛𝑐𝑠𝑡𝑒𝑝 = 𝑟𝑜𝑢𝑛𝑑 �
�2
15
−1� × 𝑚𝑑 × 𝑁𝐷𝐼𝑉
100 × 5 × 𝑀𝑂𝐷𝑃𝐸𝑅𝐼𝑂𝐷
� ,

FM_EN: enable FM by writing ‘1’.
MOD_PERIOD and INC_STEP have to be calculated using selected values of 𝑓
𝑚𝑜𝑑
and 𝑚𝑑 in order
to respect the following limitation: 𝐼𝑁𝐶 _ 𝑆𝑇𝐸𝑃 × 𝑀𝑂𝐷 _ 𝑃𝐸𝑅𝐼𝑂𝐷 ≤
(2
15
− 1).
Recommended modulation depths are ±0.25% to±4% for center spread and − 0.5% to − 8% for
down spread.
3. A device initialisation procedure
We’ve seen different steps to follow for initialising the microcontroller, we can now write a
generic initialisation function that could be used for a lot of embedded applications.
The structure of the code will remain the same for most of the embedded applications:
 Enable modes that may be used.

Make the clock configuration.

Mode configuration.

Peripheral configuration.

Transition towards a user mode.
CGM .FMPLL_MR.B.MOD_PERIOD = 20; /* fmod=50kHz */
CGM .FMPLL_MR.B.INC_STEP = 29; /* md = 0.1% */
CGM .FMPLL_MR.B.FM_EN = 1; /* enable FM */