mc9s12xs128 Freescale Semiconductor, Inc, mc9s12xs128 Datasheet - Page 252

• Manufacturer Part Number: mc9s12xs128
• Description: Hcs12 Microcontrollers 16-bit Automotive Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

S12XE Clocks and Reset Generator (S12XECRGV1)
8.4
8.4.1
8.4.1.1
The IPLL is used to run the MCU from a different time base than the incoming OSCCLK.
shows a block diagram of the IPLL.
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.
Several examples of IPLL divider settings are shown in
settings are not recommended. The following rules help to achieve optimum stability and shortest lock
time:
252
.
•
•
EXTAL
XTAL
Use lowest possible f
Use highest possible REFCLK frequency f
Supplied by:
Functional Description
Functional Blocks
Phase Locked Loop with Internal Filter (IPLL)
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.
V
V
CONSUMPTION
DDPLL
DD
OSCILLATOR
REDUCED
/V
If (PLLSEL = 1) then f
IF POSTDIV = $00 the f
SS
/V
SSPLL
OSCCLK
VCO
MONITOR
f PLL
CLOCK
/ f
S12XS Family Reference Manual, Rev. 1.10
Figure 8-15. IPLL Functional Diagram
=
REF
2 f OSC
PROGRAMMABLE
×
REFERENCE
ratio (SYNDIV value).
REFDIV[5:0]
DIVIDER
BUS
PLL
PROGRAMMABLE
= f
SYNDIV[5:0]
×
DIVIDER
is identical to f
LOOP
----------------------------------------------------------------------------- -
[
PLL
REFDIV
NOTE
REF
/ 2.
REFCLK
.
Table
SYNDIV
FBCLK
+
1
] 2 POSTDIV
[
8-14. Shaded rows indicated that these
VCO
×
DETECTOR
DETECTOR
+
PHASE
1
LOCK
PDET
(divide by one)
PROGRAMMABLE
POSTDIV[4:0]
DIVIDER
POST
]
DOWN
UP
VCOCLK
LOCK
CPUMP
FILTER
AND
Freescale Semiconductor
V
DDPLL
Figure 8-15
/V
PLLCLK
SSPLL
VCO