MC68HC908LJ12 Datasheet, PDF (111/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Clock Generator Module (CGM)
6. Select the VCO’s power-of-two range multiplier E, according to
this table:
Frequency Range
E
0 < f_VCLK < 9,830,400
0
9,830,400 ≤ f_VCLK < 19,660,800
1
19,660,800 ≤ f_VCLK < 39,321,600
2
NOTE: Do not program E to a value of 3.
7. Select a VCO linear range multiplier, L, where f_NOM = 38.4kHz
L
=
r
ou
nd



2----^E--f--V-×^---C--f-_NL^----KO----_M^{---}
8. Calculate and verify the adequacy of the VCO programmed
center-of-range frequency, f_VRS. The center-of-range frequency is
the midpoint between the minimum and maximum frequencies
attainable by the PLL.
f_VRS = (L × 2^E)f_NOM
For proper operation,
f_VRS – f_VCLK
≤ -^f-^N----^O----^M------^×-----²---^E--
2
NOTE:
9. Verify the choice of P, R, N, E, and L by comparing f_VCLK to f_VRS
and f_VCLKDES. For proper operation, f_VCLK must be within the
application’s tolerance of f_VCLKDES, and f_VRS must be as close as
possible to f_VCLK.
Exceeding the recommended maximum bus frequency or VCO
frequency can crash the MCU.
Technical Data
112
Clock Generator Module (CGM)
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor