Chapter 11 S12XE Clocks and Reset Generator (S12XECRGV1)
MC9S12XE-Family Reference Manual , Rev. 1.19
472
Freescale Semiconductor
11.3.2.2
S12XECRG Reference Divider Register (REFDV)
The REFDV register provides a finer granularity for the IPLL multiplier steps.
Read: Anytime
Write: Anytime except when PLLSEL = 1
NOTE
Write to this register initializes the lock detector bit.
The REFFRQ[1:0] bit are used to configure the internal PLL filter for optimal stability and lock time. For
correct IPLL operation the REFFRQ[1:0] bits have to be selected according to the actual REFCLK
frequency as shown in
. Setting the REFFRQ[1:0] bits wrong can result in a non functional
IPLL (no locking and/or insufficient stability).
11.3.2.3
S12XECRG Post Divider Register (POSTDIV)
The POSTDIV register controls the frequency ratio between the VCOCLK and PLLCLK. The count in the
final divider divides VCOCLK frequency by 1 or 2*POSTDIV. Note that if POSTDIV = $00 f
PLL
= f
VCO
(divide by one).
Module Base + 0x0001
7
6
5
4
3
2
1
0
R
REFFRQ[1:0]
REFDIV[5:0]
W
Reset
0
0
0
0
0
0
0
0
Figure 11-4. S12XECRG Reference Divider Register (REFDV)
Table 11-3. Reference Clock Frequency Selection
REFCLK Frequency Ranges
REFFRQ[1:0]
1MHz <= f
REF
<= 2MHz
00
2MHz < f
REF
<= 6MHz
01
6MHz < f
REF
<= 12MHz
10
f
REF
>12MHz
11
fREF
fOSC
REFDIV 1
+
(
)
------------------------------------
=
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