MC9S12P128 Datasheet, PDF (233/564 Pages) Freescale Semiconductor, Inc – S12 Microcontrollers

S12 Clock, Reset and Power Management Unit (S12CPMU) Block Description
Table 7-22. Examples of PLL Divider Settings
f_osc REFDIV[3:0] f_REF REFFRQ[1:0] SYNDIV[5:0]
off
$00
1MHz
00
$1F
off
$00
1MHz
00
$1F
off
$00
1MHz
00
$0F
4MHz
$00
4MHz
01
$03
f_VCO
64MHz
64MHz
32MHz
32MHz
VCOFRQ[1:0] POSTDIV[4:0] f_PLL
01
$03
16MHz
01
$00
64MHz
00
$00
32MHz
01
$00
32MHz
f_bus
8MHz
32MHz
16MHz
16MHz
The phase detector then compares the FBCLK with the REFCLK. Correction pulses are generated based
on the phase difference between the two signals. The loop filter then slightly alters the DC voltage on the
internal filter capacitor, based on the width and direction of the correction pulse.
The user must select the range of the REFCLK frequency (REFFRQ[1:0] bits) and the range of the
VCOCLK frequency (VCOFRQ[1:0] bits) to ensure that the correct PLL loop bandwidth is set.
The lock detector compares the frequencies of the FBCLK and the REFCLK. Therefore, the speed of the
lock detector is directly proportional to the reference clock frequency. The circuit determines the lock
condition based on this comparison.
If PLL LOCK interrupt requests are enabled, the software can wait for an interrupt request and then check
the LOCK bit. If interrupt requests are disabled, software can poll the LOCK bit continuously (during PLL
start-up, usually) or at periodic intervals. In either case, only when the LOCK bit is set, the VCOCLK will
have stabilized to the programmed frequency.
• The LOCK bit is a read-only indicator of the locked state of the PLL.
• The LOCK bit is set when the VCO frequency is within a certain tolerance, ∆_Lock, and is cleared
when the VCO frequency is out of a certain tolerance, ∆_unl.
• Interrupt requests can occur if enabled (LOCKIE = 1) when the lock condition changes, toggling
the LOCK bit.
7.4.2 Startup from Reset
An example of startup of clock system from Reset is given in Figure 7-32.
S12P-Family Reference Manual, Rev. 1.12
Freescale Semiconductor
233