Author Topic: replace 3.58MHz with 3.579545MHz  (Read 5548 times)

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Offline ifrenideTopic starter

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Re: replace 3.58MHz with 3.579545MHz
« Reply #25 on: January 04, 2020, 02:17:34 am »
the exact 3.58 MHz exist in ceramic or passive crystal.
I want to know what is the  MAX tolerance or close replacement of crystals in microcontroller application?
Can we for example replace 4MHz with 12 MHz if we can't why?
I want limits of internal circuitary of microcontrollers "timmers" when we use external crystals, how can a value like  3.579545MHz will be usefull while there is a pre defined prescale timming.we can't get for example 2546.5 clock in digital electronics so ,I think that there is a hardware limit for crystal application.
best regards
 

Offline amyk

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Re: replace 3.58MHz with 3.579545MHz
« Reply #26 on: January 04, 2020, 04:28:06 am »
You would have to look up the specifications of the components and take into account the firmware of the system too. There is no general answer.
 

Offline ifrenideTopic starter

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Re: replace 3.58MHz with 3.579545MHz
« Reply #27 on: January 04, 2020, 08:29:50 am »
thank you amyk.
 

Offline Kilrah

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Re: replace 3.58MHz with 3.579545MHz
« Reply #28 on: January 04, 2020, 12:21:42 pm »
Without knowing what the program on the device is doing it's impossible to say. If the program uses that as reference for precise timing then it can be a problem, if not it won't care a single bit.
 

Offline CatalinaWOW

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Re: replace 3.58MHz with 3.579545MHz
« Reply #29 on: January 04, 2020, 05:12:53 pm »
Amyk is correct.  To do this correctly you have to evaluate both the parts involved and the purpose you will put them to. 

If you want some general rules of thumb I would give you the following:

1.  If your goal is just to get the processor running you will be generally safe with crystals with 10-25% of the nominal design (more on the low end, less on the high.  You may be successful with much larger departures but the odds go down the further you go.  Again, data sheets are your friend.

2.  If you are doing PWM and other similar processes with your processor things will generally work with small variations (again 10-25%) from the nominal value.  But be prepared for odd cases that don't work, and behavior that is not optimal.

3.  If you are doing clocks and timers you really do have to be guided by the needs of your application.  While some of these applications may be OK with a few percent error, others will demand errors that are a tiny fraction of a percent.
 

Offline mikeselectricstuff

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Re: replace 3.58MHz with 3.579545MHz
« Reply #30 on: January 04, 2020, 05:50:16 pm »
If its just a Z80 clock I cant see why any xtal around that speed wont do.
Unless the same xtal drives a UART or some other time critical device.
UART comms can accommodate a total ( tx+rx) error of at least 4%, so the ~0.01% error would be insignificant.
For anything other than long-term timekeeping or frequency measurement, 0.01% error is well below the weeds
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Offline westfw

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Re: replace 3.58MHz with 3.579545MHz
« Reply #31 on: January 07, 2020, 07:52:21 am »
Note that the difference is about 0.01%, which is less than the tolerance of the ceramic resonators used in many modern designs, and probably on the same order as the tolerance of random cheap crystals that you buy from China.It's really hard for me to imagine a "normal" application that would care about that level of error.
 


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