DSP56F803 Motorola Inc, DSP56F803 Datasheet - Page 23

• Manufacturer Part Number: DSP56F803
• Description: 16-bit Hybrid Controller
• Manufacturer: Motorola Inc

3.5 External Clock Operation
The 56F803 system clock can be derived from an external crystal or an external system clock signal. To
generate a reference frequency using the internal oscillator, a reference crystal must be connected between
the EXTAL and XTAL pins.
3.5.1
The internal oscillator is also designed to interface with a parallel-resonant crystal resonator in the
frequency range specified for the external crystal in
oscillator circuit is shown. Follow the crystal supplier’s recommendations when selecting a crystal,
because crystal parameters determine the component values required to provide maximum stability and
reliable start-up. The crystal and associated components should be mounted as close as possible to the
EXTAL and XTAL pins to minimize output distortion and start-up stabilization time. The internal 56F80x
oscillator circuitry is designed to have no external load capacitors present. As shown in
external load capacitors should be used.
The 56F80x components internally are modeled as a parallel resonant oscillator circuit to provide a
capacitive load on each of the oscillator pins (XTAL and EXTAL) of 10pF to 13pF over temperature and
process variations. Using a typical value of internal capacitance on these pins of 12pF and a value of 3pF as
a typical circuit board trace capacitance the parallel load capacitance presented to the crystal is 9pF as
determined by the following equation:
56F803 Technical Data
IFREN
XADR
ERASE
NVSTR
MAS1
YE=SE=OE=0
XE
Crystal Oscillator
CL =
Tnvs
CL1 * CL2
CL1 + CL2
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 8. Flash Mass Erase Cycle
Go to: www.freescale.com
+ Cs =
12 * 12
12 + 12
Tme
Table
+ 3 = 6 + 3 = 9pF
27. In
Figure 9
External Clock Operation
a recommended crystal
Tnvh1
Figure 10
Trcv
no
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