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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
11-10
Freescale Semiconductor
shows clock mode selection for the MPC5553 208 pin package.
11.1.4.1
Crystal Reference (Default Mode)
In crystal reference mode, the FMPLL receives an input clock frequency (F
ref_crystal)
from the crystal
oscillator circuit (and, in the MPC5553, the pre-divider) and multiplies the frequency to create the FMPLL
output clock. The user must supply a crystal oscillator that is within the appropriate input frequency range,
the crystal manufacture’s recommended external support circuitry, and a short signal route from the MCU
to the crystal.
The external support circuitry for the crystal oscillator is shown in
. Example component
values are shown as well. Note that the actual circuit should be reviewed with the crystal manufacturer. A
block diagram illustrating crystal reference mode is shown in
Figure 11-7. Crystal Oscillator Network
In crystal reference mode, the FMPLL can generate a frequency modulated clock or a non-modulated
clock (locked on a single frequency). The modulation rate, modulation depth, output clock divide ratio
(RFD), and whether the FMPLL is modulating or not can be programmed by writing to the FMPLL
registers. Crystal reference is the default clock mode for the MPC5554 and for the 324 and 416 packages
of the MPC5553. It is not necessary to force PLLCFG[0:1] to enter this mode. In the 208 package size,
because it has no RSTCFG pin, the crystal reference mode can only be selected through the PLLCFG pins.
Table 11-2. Clock Mode Selection in 208 Pin Package
Package Pins
Clock Mode
Synthesizer Status Register
(FMPLL_SYNSR)
1
Bits
1
Section 11.3.1.2, “Synthesizer Status Register (FMPLL_SYNSR)
” for more information on these
bits.
PLLCFG[0]
PLLCFG[1]
MODE
PLLSEL
PLLREF
1
0
Crystal Reference
(default mode)
1
1
1
0
1
External Reference
1
1
0
0
0
Bypass 0
0
0
1
1
Dual-Controller 1
0
0
V
SSSYN
C2
EXTAL
XTAL
V
SSSYN
C1
Crystal
RF
On Chip
Содержание MPC5553
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