Ant_Magma said:
Thx Chris, i've already read the datasheets and the reference designs.
I'm not lazy, i'm just new.
I'm confused becoz the datasheet says to connect the oscillator to X1
and leave X2 open. And yet in the circuit its connecting both X1 and X2
like you showed in your post. So which is which?
This is very common.
X1 and X2 are connected (internally) to an oscillator amplifier.
if you are using a crystal, then the crystal is connected across X1 and
X2. Alternatively, *if you happen to have a 25MHz clock available and
wish to use it for this chip*, then connect the clock (from somewhere
else in the system) to X1 and leave X2 open.
In terms of the device, X1 is the input to the oscillator, X2 is it's
output.
So if you are using a crystal, connect it as shown.
Here's what the datasheet says:
(P25 in acrobat reader. P26 of datasheet)
[Highlights mine]
3.7 Crystal Oscillator Circuit
The DsPHYTER II supports an external CMOS level oscillator source or a
crystal resonator device. *****If an external clock source is used, X1
should be tied to the clock source and X2 should be left
floating******. In either case, the clock source must be a 25 MHz
0.005% (50 PPM) CMOS oscillator or a 25 MHz (50 PPM), parallel, 20 pF
load crystal resonator.
Figure 10 below shows a typical connection for a crystal resonator
circuit. The load capacitor values will vary with the crystal vendors;
check with the vendor for the recommended loads.
The oscillator circuit was designed to drive a parallel resonance AT
cut crystal with a minimum drive level of 500µW and a maximum of 1mW.
If a crystal is specified for a lower
drive level, a current limiting resistor should be placed in series
between X2 and the crystal.
As a starting point for evaluating an oscillator circuit, if the
requirements for the crystal are not known, CL1 and CL2 should be set
at 22 pF, and R1 should be set at 0Ω.
Cheers
PeteS