DSP56F803EVM Freescale Semiconductor, DSP56F803EVM Datasheet - Page 27

• Manufacturer Part Number: DSP56F803EVM
• Description: KIT EVALUATION FOR DSP56F803
• Manufacturer: Freescale Semiconductor

Specifications of DSP56F803EVM

• Processor To Be Evaluated: 56F803
• Data Bus Width: 16 bit
• Interface Type: RS-232, JTAG
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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
Figure 3-8
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:
This is the value load capacitance that should be used when selecting a crystal and determining the actual
frequency of operation of the crystal oscillator circuit.
Freescale Semiconductor
Crystal Oscillator
no external load capacitors should be used.
CL =
Figure 3-7 Connecting to a Crystal Oscillator
EXTAL XTAL
CL1 * CL2
CL1 + CL2
R
f
c
z
56F803 Technical Data, Rev. 16
+ Cs =
Recommended External Crystal
Parameters:
R
f
c
z
= 8MHz (optimized for 8MHz)
= 1 to 3 MΩ
12 * 12
12 + 12
Table
3-9. In
+ 3 = 6 + 3 = 9pF
Figure 3-7
a recommended crystal
External Clock Operation
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