mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 117

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

MC68HC16Y3/916Y3
USER’S MANUAL
For the device to perform correctly, both the clock frequency and VCO frequency
(selected by the W, X, and Y bits) must be within the limits specified for the MCU. In
order for the VCO frequency to be within specifications (less than or equal to the
maximum system clock frequency multiplied by two), the X bit must be set for system
clock frequencies greater than one-half the maximum specified system clock.
Internal VCO frequency is determined by the following equations:
On both slow and fast reference devices, when an external system clock signal is
applied (MODCLK = 0 during reset), the PLL is disabled. The duty cycle of this signal
is critical, especially at operating frequencies close to maximum. The relationship
between clock signal duty cycle and clock signal period is expressed as follows:
Table 5-2 shows 16.78 MHz clock control multipliers for all possible combinations of
SYNCR bits. To obtain clock frequency, find counter modulus in the leftmost column,
then multiply the reference frequency by the value in the appropriate prescaler cell.
Refer to APPENDIX A ELECTRICAL CHARACTERISTICS for maximum allowable
clock rate.
Table 5-3 shows actual 16.78 MHz clock frequencies for the same combinations of
SYNCR bits. To obtain clock frequency, find counter modulus in the leftmost column,
then refer to appropriate prescaler cell. Refer to APPENDIX A ELECTRICAL CHAR-
ACTERISTICS for maximum system frequency (f
Minimum External Clock Period
----------------------------------------------------------------------------------------------------------------------------------------------------------------------- -
50% Percentage Variation of External Clock Input Duty Cycle
–
Freescale Semiconductor, Inc.
For More Information On This Product,
Minimum External Clock High/Low Time
Go to: www.freescale.com
f
f
VCO
VCO
=
=
2f
4f
or
sys
sys
=
if X = 0
if X = 1
sys
).
MOTOROLA
5-9