mc68hc908qz16 Freescale Semiconductor, Inc, mc68hc908qz16 Datasheet - Page 64

• Manufacturer Part Number: mc68hc908qz16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Clock Generator Module (CGM)
64
10. Verify the choice of N, E, and L by comparing f
4. Select a VCO frequency multiplier, N.
5. Calculate and verify the adequacy of the VCO and bus frequencies f
6. Select the VCO’s power-of-two range multiplier E, according to
7. Select a VCO linear range multiplier, L, where f
8. Calculate and verify the adequacy of the VCO programmed center-of-range frequency, f
9. For proper operation,
In cases where desired bus frequency has some tolerance, choose f
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
Specifications. After choosing N, the actual bus frequency can be determined using equation in 2
above.
center-of-range frequency is the midpoint between the minimum and maximum frequencies
attainable by the PLL.
f
to f
VCLK
VCLK
must be within the application’s tolerance of f
.
Exceeding the recommended maximum bus frequency or VCO frequency
can crash the MCU.
1. Do not program E to a value of 3.
MC68HC908GZ16 • MC68HC908GZ8 Data Sheet, Rev. 4
Table 4-2. Power-of-Two Range Selectors
16 MHz< f
8 MHz< f
Frequency Range
0 < f
N
L = Round
f
VRS
VCLK
=
f
VCLK
f
VCLK
f
VCLK
VRS
BUS
round
–
≤ 8 MHz
f
≤ 16 MHz
VCLK
= (L x 2
≤ 32 MHz
=
=
NOTE
⎛
⎜
⎝
( ) f
(
f
------------------------- -
N
f
VCLKDES
VCLK
≤
f
2
VCLK
RCLK
NOM
E
×
E
f
-------------------------- -
f
NOM
) f
VCLK
x f
VCLKDES
RCLK
) 4 ⁄
NOM
= 71.4 kHz
to f
NOM
2
×
⎞
⎟
⎠
VRS
2
E
, and f
and f
Table
VRS
VCLKDES
2
E
0
1
(1)
Chapter 21 Electrical
VCLK
RCLK
must be as close as possible
4-2.
. For proper operation,
to a value determined
and f
Freescale Semiconductor
BUS
.
VRS
. The