dsp56853 Freescale Semiconductor, Inc, dsp56853 Datasheet - Page 29

• Manufacturer Part Number: dsp56853
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

4.5 External Clock Operation
The 56853 system clock can be derived from a 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.
4.5.1
The internal oscillator is designed to interface with a parallel-resonant crystal resonator in the frequency
range specified for the external crystal in
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.
4.5.2
The recommended method of connecting an external clock is given in
source is connected to XTAL and the EXTAL pin is held at ground, V
bit in CGM must be set to 0.
4.5.3
The recommended method of connecting an external clock is given in
source is connected to XTAL and the EXTAL pin is held at V
set to 0.
Freescale Semiconductor
Figure 4-7 Connecting a High Speed External Clock Signal using XTAL
Crystal Oscillator
High Speed External Clock Source (> 4MHz)
Low Speed External Clock Source (2-4MHz)
Crystal Frequency = 2–4 MHz (optimized for 4MHz)
EXTAL XTAL
R
z
Figure 4-6 Crystal Oscillator
(up to 240MHz)
56853 Technical Data, Rev. 6
External
Table
Clock
XTAL
Sample External Crystal Parameters:
R
TOD_SEL bit in CGM must be set to 0
DSP56853
z
= 10MΩ
4-6. In
EXTAL
GND,
or V
Figure 4-6
DDA
V
DDA
DDA
/2
,
/2. The TOD_SEL bit in CGM must be
a typical crystal oscillator circuit is
DDA
Figure
Figure
, or V
4-7. The external clock
4-8. The external clock
DDA
/2. The TOD_SEL
External Clock Operation
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