Chapter 11 S12XE Clocks and Reset Generator (S12XECRGV1)
MC9S12XE-Family Reference Manual , Rev. 1.19
484
Freescale Semiconductor
11.4
Functional Description
11.4.1
Functional Blocks
11.4.1.1
Phase Locked Loop with Internal Filter (IPLL)
The IPLL is used to run the MCU from a different time base than the incoming OSCCLK.
shows a block diagram of the IPLL.
Figure 11-15. IPLL Functional Diagram
For increased flexibility, OSCCLK can be divided in a range of 1 to 64 to generate the reference frequency
REFCLK using the REFDIV[5:0] bits. This offers a finer multiplication granularity. Based on the
SYNDIV[5:0] bits the IPLL generates the VCOCLK by multiplying the reference clock by a multiple of
2, 4, 6,... 126, 128. Based on the POSTDIV[4:0] bits the VCOCLK can be divided in a range of 1,2,4,6,8,...
to 62 to generate the PLLCLK.
.
NOTE
Although it is possible to set the dividers to command a very high clock
frequency, do not exceed the specified bus frequency limit for the MCU.
If (PLLSEL = 1) then f
BUS
= f
PLL
/ 2.
IF POSTDIV = $00 the f
PLL
is identical to f
VCO
(divide by one)
Several examples of IPLL divider settings are shown in
. Shaded rows indicated that these
settings are not recommended. The following rules help to achieve optimum stability and shortest lock
time:
•
Use lowest possible f
VCO
/ f
REF
ratio (SYNDIV value).
•
Use highest possible REFCLK frequency f
REF
.
REDUCED
CONSUMPTION
OSCILLATOR
EXTAL
XTAL
OSCCLK
PLLCLK
REFERENCE
PROGRAMMABLE
DIVIDER
PDET
PHASE
DETECTOR
REFDIV[5:0]
LOOP
PROGRAMMABLE
DIVIDER
SYNDIV[5:0]
VCO
LOCK
UP
DOWN
LOCK
DETECTOR
REFCLK
FBCLK
V
DDPLL
/V
SSPLL
CLOCK
MONITOR
V
DDPLL
/V
SSPLL
V
DD
/V
SS
Supplied by:
CPUMP
AND
FILTER
POST
PROGRAMMABLE
DIVIDER
POSTDIV[4:0]
VCOCLK
fPLL 2 fOSC
SYNDIV 1
+
REFDIV 1
+
[
]
2 POSTDIV
×
[
]
------------------------------------------------------------------------------
×
×
=
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages
