MC68HC908GP32 Datasheet, PDF (116/410 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Freescale Semiconductor, Inc.
Clock Generator Module (CGMC)
Technical Data
114
P, the power of two multiplier, and N, the range multiplier, are
integers.
In cases where desired bus frequency has some tolerance,
choose f_RCLK to a value determined either by other module
requirements (such as modules which are clocked by CGMXCLK),
cost requirements, or ideally, as high as the specified range
allows. See Section 23. Electrical Specifications. Choose the
reference divider, R = 1. After choosing N and P, the actual bus
frequency can be determined using equation in 2 above.
When the tolerance on the bus frequency is tight, choose f_RCLK to
an integer divisor of f_BUSDES, and R = 1. If f_RCLK cannot meet this
requirement, use the following equation to solve for R with
practical choices of f_RCLK, and choose the f_RCLK that gives the
lowest R.
R
=
round
R_MAX
×






f--_{V----fC--R--L--C-K--L-D--K--E----S- }
–
in
te
ge
r



-f-^V----f^C--_R--^L--_C-^K--_L-^D--_K--^E----^S- _{}



4. Select a VCO frequency multiplier, N.
N
=
r
ou
nd



R------×_{-----ff--VR----CC---L-L--K-K---D----E---S--}
Reduce N/R to the lowest possible R.
5. If N is < N_max, use P = 0. If N > N_max, choose P using this table:
Current N Value
P
0 < N ≤ Nmax
0
Nmax < N ≤ Nmax × 2
1
Nmax × 2 < N ≤ Nmax × 4
2
Nmax × 4 < N ≤ Nmax × 8
3
Then recalculate N:
N
=
ro
u
nd



-R----f-^×-_R---_C-f--^V-_L---^CK----^L-_×-^K----2^D---_P-^E---^S--_{}
MC68HC908GP32•MC68HC08GP32 — Rev. 6
Clock Generator Module (CGMC)
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