DSP56721 Freescale Semiconductor, Inc, DSP56721 Datasheet - Page 13

• Manufacturer Part Number: DSP56721
• Description: Dsp56721 Multi-core Audio Processor
• Manufacturer: Freescale Semiconductor, Inc

2.1.7
The DSP56720/DSP56721 system clock is derived from the on-chip oscillator or is externally supplied. To use the on-chip
oscillator, connect a crystal and associated resistor/capacitor components to EXTAL and XTAL; see the example in
If the DSP56720/DSP56721 system clock is an externally supplied square wave voltage source, it is connected to EXTAL
(Figure
Freescale Semiconductor
10). When the external square wave source is connected to EXTAL, the XTAL pin is not used.
C
EXTAL
Note:
External Clock Operation
EXTAL
The midpoint is 0.5 (V
XTAL1
Symphony
R
V
IL
XTAL
ETH
TM
C
DSP56720 / DSP56721 Multi-Core Audio Processors, Rev. 3
1
Figure 9. Using the On-Chip Oscillator
Figure 10. External Clock Timing
IH
Suggested component values:
Fosc = 24.576 MHz
R = 1 M ±10%
C (EXTAL)= 18 pF
C (XTAL) = 18 pF
Calculations are for a 5 – 30 MHz crystal with the following parameters:
• Shunt capacitance (C
• Series resistance 40 Ohm
• Drive level of 10 μW
+ V
3
ETL
IL
).
2
ETC
0
) of 10 pF – 12 pF
Midpoint
V
IH
Figure
9.
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