how to generate 10M input to the CLKIN pin?

[lei]

Is there a simple way to get a 10M CLK signal, I need that to connect to the CLKIN pin of the chip. what is the circuit design like?
can anyone help?

 

[Bartart]

Hi!

use quartz oscilator, see if it is voltage compatible with the IO and enjoy!



For the circuit search google every digital device use it and it is very simple, as I said before be careful about IO pin voltage.

Good luck, bart

 

[mrcube_ns]

Bartart is right, most simplest way is with quartz.

You can make ring oscillator with CMOS gates (odd number of invertors).

Maybe some hi speed op amp.


Hope its helps.


Mr.Cube

 

[lei]

Thanks to Bartart and mrcube_ns.

when I search for crystal oscillator online, I find there are two types, one have 4 pins and the other have 2 pins.
the 2 pins crystal seems simple to me, the schematic diagram shows that I just need to connect the 2 pins of the crystal to the XTAL1 and XTAL2 pins of the processor respectively, and also connect to ground through two capacitor respectively.

I am just wondering whether my understanding of the schematic is right or not, can anyone give some hints?
and also how about the value of the crystal, equal to 10MHz, or 5 MHz?

 

[mrcube_ns]

Yes you understand well. I suggest 2 pins 10MHz crystal with 2 caps. Those two caps is for stabilizing frequency (I suggest 22pF or 27pF).


Mr.Cube

 

[fishpapa]

one example.

 

[lei]

Thanks to mrcube_ns and fishpapa,

fishpapa,
what is the function of R1? the value is equal to 10M, it seems quite large, is it very necessary to put R1 there?

 

[Big Boy]

The R1 only purpose it at startup, when the circuit is powered-up. It help the crystal to enter oscillation. Usually, you can omit it, but sometimes, it can happen that you get problems, with some circuits, where the oscillator won't start properly. It will either take a long time to start to oscillate or even not start at all. This doesn't happen often, or for every circuit types, but it's good practice to put a resistor.

The resistor must be of high value. It is normal for it to be 10Meg. This is because the crystal itself have a very high impedance (away from it's resonating frequency). And if you put R too low, the circuit may not oscilate at the crystal frequency, but in plain free-running mode (a much higher, uncontroled frequency, unsuitable for the application).

 

[Fom]

It is supposed to be an inverter connected between RTX1 and RTX0. The R1 make this inverter operate like inverting amplifier and provide DC bias for input of this amplifier.

 

[FANT]

If you use a ceramic resonator use a 1 KOhm resistor between RTXO end R1.
Also, for example on RS catalog the crystal oscillators are sold fro about 5 Euro, simple crystals at 10 MHz for 3 Euro.

Mandi

 

[moira]

if u need 10mhz crystal,
i don't think the resistor is necessary.
and if th dependability of ur system is required very strict,
i suggest Voltage Controlled Crystal Oscillator (VCO, 4 pins).

 

[lcg22]

I just have aquestion on VCO/VCXO. Who can tell me what is the difference between frequency stability and frequency accuracy?

 

[Noman Yousaf]

very simple way is to get 10Mhz use one NAND gate
(cd4011)
connect 10MHz XTL between in and out of NAND.(Just short the both input lines)
connect 1 10Mega ohm resistor in paralle of XTL.
2 33P capacitors from both pins of XTL to GND.
and get 10MHz frequency from output of NAND gate