MC68HC908GR8A_07 Datasheet, PDF (61/260 Pages) Freescale Semiconductor, Inc – Microcontrollers

Functional Description
10. 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.
NOTE
Exceeding the recommended maximum bus frequency or VCO frequency
can crash the MCU.
11. Program the PLL registers accordingly:
a. In the PRE bits of the PLL control register (PCTL), program the binary equivalent of P.
b. In the VPR bits of the PLL control register (PCTL), program the binary equivalent of E.
c. In the PLL multiplier select register low (PMSL) and the PLL multiplier select register high
(PMSH), program the binary equivalent of N.
d. In the PLL VCO range select register (PMRS), program the binary coded equivalent of L.
e. In the PLL reference divider select register (PMDS), program the binary coded equivalent
of R.
Table 4-1 provides numeric examples (numbers are in hexadecimal notation):
Table 4-1. Numeric Example
f_BUS (MHz)
2.0
4.0
8.0
2.0
4.0
8.0
2.4576
4.9152
7.3728
2.0
4.0
8.0
f_RCLK (MHz)
8.0
8.0
8.0
4.0
4.0
4.0
4.9152
4.9152
4.9152
8.0
8.0
8.0
PCTL
P
E
0
0
0
1
0
2
0
0
0
1
0
2
0
1
0
2
0
2
0
0
0
1
0
2
PMSH,L
N
008
010
020
002
004
008
002
004
006
001
002
004
PMRS
L
D0
D0
D0
D0
D0
D0
80
80
C0
D0
D0
D0
PMDS
R
8
8
8
1
1
1
1
1
1
1
1
1
MC68HC908GR8A • MC68HC908GR4A Data Sheet, Rev. 5
Freescale Semiconductor
61