AC Electrical Characteristics
2.5.2 External Clock Operation
The DSP56301 system clock is derived from the on-chip oscillator or it is externally supplied. To use the on-chip
oscillator, connect a crystal and associated resistor/capacitor components to EXTAL and XTAL; examples are
shown in Figure 2-1.
EXTAL
XTAL
Suggested Component Values:
f = 4 MHz
OSC
R
f
= 20 MHz
OSC
R = 680 kΩ 10%
C = 56 pF 20%
Note: Make sure that in
the PCTL Register:
R = 680 kΩ 10%
C = 22 pF 20%
•
•
XTLD (bit 16) = 0
If f > 200 kHz,
XTLR (bit 15) = 0
Calculations were done for a 4/20 MHz crystal
with the following parameters:
OSC
C
XTAL1
C
•
•
•
•
C of 30/20 pF,
L
Fundamental Frequency
Crystal Oscillator
C of 7/6 pF,
0
series resistance of 100/20 Ω, and
drive level of 2 mW.
Figure 2-1. Crystal Oscillator Circuits
If an externally supplied square wave voltage source is used, disable the internal oscillator circuit during boot-up
by setting XTLD (PCTL Register bit 16 = 1—see the DSP56301 User’s Manual). The external square wave source
connects to EXTAL; XTAL is not physically connected to the board or socket. Figure 2-2 shows the relationship
between the EXTAL input and the internal clock and CLKOUT.
V
Midpoint
IHX
EXTAL
ET
ET
H
V
L
Note:
The midpoint is
0.5 (V + V ).
ILX
2
3
IHX
ILX
4
ET
C
5
5
CLKOUT with
PLL disabled
7
CLKOUT with
PLL enabled
7
6a
6b
Figure 2-2. External Clock Timing
DSP56301 Technical Data, Rev. 10
Freescale Semiconductor
2-5
FREESCALE [ Freescale ]
