40MHz crystal works on 13.33MHz?

[cdcll]

.pdf crystal 3rd overtone trap frequency

I would like to make the MCU W77E58 work on 40MHz, but my oscilloscope show the crystal works on 13.33MHz, why?
anyone can help me how to solve it? Thanks!

 

[cancel]

40mhz xtal

hi .. lots quartz above 10mhz works at overtone frequencies .. e.g. 50mhz is 5th overtone of 10mhz bas freq quarts ... your case is 3rd overtone

regards

cancel

 

[cdcll]

problems with 5th overtone crystals

Hello cancel,

Thanke you for your quick reply! and as you said, my case is 3rd overtone, but how can I make it work on 40MHz? Could you give me detail suggestions?

BR,
cdcll

 

[cancel]

12 mhz crystal how do they work

i am not sure .. i would make tuned circuit for 40mhz and connect it as clock signal ..

 

[pool_77]

40mhz xtal pdf

try to make capacitors smaller

 

[Slw]

40 mhz xtal

Try with another crystal. There are serial and parallel types and maybe your MCU accepts only one of the types. Try to make external generator with 7400.

 

[sick_man]

oscillator 7400 quartz 10mhz

to use xtal above 30 mhz you need to add a xtal cage to any pcb design

or as above says construct a separate oscillator
avoid however a 7400 as its max bandwidth is 20mhz {on a good day}

instead use a xtal oscillator in a can {square 4 pins}
any oscillator above 20 mhz i have seen works this way for high speed risc

OR it is built is a square caged off grounplaned pcb foil area
and the xtal its self is just a "chip xtal" made of glass with the xtal embeded and also has 4 pins so i guess is a mini type of the metal cass veriety

with the square case output
you need supply only one {clock in pin} pin of the micro direct or via a 10 pf cap


mostly none of this matters with overtone xtals
you basicaly dont have the right type
but there is too many uncertanty surround your grounplane
and xtal cage {pcb foils planes etc} as these are realy realy needed
to get a clean 40mhz
however the scope will only show you the biggest carrier
i hate overtones carriers interspersed with the freq you need
this is why i suggest the square can type
as there makers pride themself's on clean output at a fundimental freq it says it is

an example is just about any 386 motherboard will have a 30 mhz or a 20 mhz one ... they are everywhere
so the rule must be reuse old one's

there spec is easy to find and they have a common standard of pinout

from such a can type you can drive 20 chips clocks needs with no problems
or buffer chips
adding further buffer will many more....

 

[sick_man]

overtone 7400

another thing that worries me is 13.33mhz

this is a strange freq

as thou the xtal has wondered badly

try simply turing it round

and as a general point to note

the other week a pal brought his old nintendo with three sick cargtiges

after i opened the cardrige i notice a resosonator

so i turn it the other way round

pluged in the first and away the game went

simply with time the freq had shifted
becouse atomic migrations had moved the impuritys in the devices materials all to one end

so now that cartride will work for a few years

same goes for most radios and other micro driven stuff


if it dosnt work or is a bit tempremental
check by turning the clock device {xtal or resonator} round the other way

works for video recorder micros infact any
even some computers 8bit work again properly when this is done

esp low voltage devices like keyfob for the car door

why get a new one {symptoms is well it used to work ok then it was intermittent then it stoped i changed the battery but still it dosnt work}

turn the resonator round and it will

the symantic is this

a frozen river will carry bigger bolders and half the streams bed along with it while a warm river only carries a few a few feet
a very warm river will carry more becouse warm water flows faster{is more viscuos ??spelling may be bad}
so when you expose these devices to temps like winter and summer
the impuritys dislodge faster into the river of 4mhz

 

[M!k]

xtal tank model overtone

You have to order that crystal correctly. Take a look at this datasheet:
**broken link removed**
you'll see that a 40MHz-crystal is available in the fundamental mode (40MHz) AND as 3rd overtone crystal. Both crystals are labeled "40MHz". So just specify in your order "fundamental" - then it should work.
For higher frequencies > 48 MHz only overtone crystals are available, thats right.
P.S.: it does not depend on the load capacitance ("parallel" or "serial"). This just influences the accuracy a little bit .


Regards
Mik

 

[cdcll]

7400 xtal osc

Dear all,

My supplier said the crystal I used is 3rd overtone, and they do not have the fundamental mode crystal > 30MHz.
I have tried to make the capacitors smaller(5pF), and put a parallel resistor(6.8K) to the crystal, but it still work on 13.33MHz! Could you suggest a tune method(adjust the capacitors & resistor?) to make it work properly?
I think the crystal should be OK for 40MHz, and I have to modify my design, otherwise the overtone crystals have no use? I understand that it will have no such problem if I use an oscillator instead of the crystal, but now that I encounter this problem, I would like to find it out to improve myself.
I am looking forword to your suggestions.

Best regards,
cdcll

 

[E-design]

40 mhz crystal clock

Hi

The best way is to try and prevent it from oscillating at the fundamental 13.33MHz by introducing some losses by means of a trap at this frequency to gnd or serie band pass.

For your frequency a 1.2uH inductor and a 120pF capacitor in serie connected somewhere in the feedback path to gnd will resonate at about 13.33MHz.

Another way is to place a 1.2uH inductor and 12pF capacitor in serie with the crystal. The circuit will then more readily oscilate at the harmonic freq of 40MHz.

Using a tank circuit tuned to 40MHz when you use a transistor oscillating stage will increase the gain at that frequency and lower it outside this band.

This is very common with some older CB crystals where if you try and run the crystal not in the proper configuration it will oscilate at the 1/3 of the 27MHz.

E

 

[sick_man]

how xtal crystal works

comeon

go get a 40 mhz can type +5v supply one connection to gnd pull the osc switching pin high

and out comes 40mhz only

save yourself the grief with tuned circuits