s908ab32ag0cfue Freescale Semiconductor, Inc, s908ab32ag0cfue Datasheet - Page 139

• Manufacturer Part Number: s908ab32ag0cfue
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

9.4.2.5 Special Programming Exceptions
MC68HC908AB32
Freescale Semiconductor
NOTE:
—
Rev. 1.1
Exceeding the recommended maximum bus frequency or VCO
frequency can cause the MCU to “crash”.
The programming method described in
does not account for two possible exceptions — a value of zero for N or
L is meaningless when used in the equations given. To account for these
exceptions:
7. Calculate and verify the adequacy of the VCO programmed
8. Verify the choice of N and L by comparing f
9. Program the PLL registers accordingly:
center-of-range frequency f
f
application’s tolerance of f
possible to f
VCLKDES
a. In the upper 4 bits of the PLL programming register (PPG),
b. In the lower 4 bits of the PLL programming register (PPG),
5. Calculate and verify the adequacy of the VCO and bus
6. Select a VCO linear range multiplier, L.
Clock Generator Module (CGM)
program the binary equivalent of N.
program the binary equivalent of L.
frequencies f
where f
. For proper operation, f
VCLK
NOM
.
= 4.9152MHz
VCLK
and f
VCLKDES
VRS
f
VCLK
f
BUS
f
BUS
VRS
.
L
VCLK
9.4.2.4 Programming the PLL
.
=
=
=
= (L)f
, and f
round
(
N f
f
must be within the
Clock Generator Module (CGM)
VCLK
×
NOM
VRS
RCLK


)
VCLK
f
------------ -
f
4 ⁄
VCLK
must be as close as
NOM
to f


VRS
Technical Data
and
139