MC68HC16Z1CAG16 Datasheet, PDF (111/500 Pages) Freescale Semiconductor, Inc – M68HC16Z Series users manual

Freescale Semiconductor, Inc.
5.3.1 Clock Sources
The state of the clock mode (MODCLK) pin during reset determines the system clock
source. When MODCLK is held high during reset, the clock synthesizer generates a
clock signal from an external reference frequency. The clock synthesizer control reg-
ister (SYNCR) determines operating frequency and mode of operation. When MOD-
CLK is held low during reset, the clock synthesizer is disabled and an external system
clock signal must be driven onto the EXTAL pin.
The input clock, referred to as f_ref, can be either a crystal or an external clock source.
The output of the clock system is referred to as f_sys. Ensure that f_ref and f_sys are within
normal operating limits.
To generate a reference frequency using the crystal oscillator, a reference crystal
must be connected between the EXTAL and XTAL pins. Typically, a 32.768-kHz crys-
tal is used for a slow reference, but the frequency may vary between 25 kHz to 50 kHz.
Figure 5-3 shows a typical circuit.
C1
22 pF*
C2
22 pF*
R1
330K
R2
10M
XTAL
EXTAL
V_SSI
* RESISTANCE AND CAPACITANCE BASED ON A TEST CIRCUIT CONSTRUCTED WITH A DAISHINKU DMX-38 32.768-kHz CRYSTAL.
SPECIFIC COMPONENTS MUST BE BASED ON CRYSTAL TYPE. CONTACT CRYSTAL VENDOR FOR EXACT CIRCUIT.
32 OSCILLATOR
Figure 5-3 Slow Reference Crystal Circuit
A 4.194-MHz crystal is typically used for a fast reference, but the frequency may vary
between one MHz up to six MHz. Figure 5-4 shows a typical circuit.
C1
27 PF*
C2
27 PF*
R1
1.5KΩ
R2
1MΩ
XTAL
EXTAL
V_SSI
* RESISTANCE AND CAPACITANCE BASED ON A TEST CIRCUIT CONSTRUCTED WITH A KDS041-18 4.194 MHz CRYSTAL.
SPECIFIC COMPONENTS MUST BE BASED ON CRYSTAL TYPE. CONTACT CRYSTAL VENDOR FOR EXACT CIRCUIT.
Figure 5-4 Fast Reference Crystal Circuit
16 OSCILLATOR 4M
M68HC16 Z SERIES
SYSTEM INTEGRATION MODULE
USER’S MANUAL
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5-5
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