If microcontroller has a 20MHz crystal.

How fast it can read the input signal ?

 

hi champ,
Your question is poorly defined.
Which type of input signal and what do you mean by 'read'.?
E

 

And what kind of microcontroller is it?

 

hi champ,
Your question is poorly defined.
Which type of input signal and what do you mean by 'read'.?
E

And what kind of microcontroller is it?

PIC controller like PIC16f877, PIC16f877a

My doubt is if the 40MHz digital signal applied to the input pin of the microcontroller.

Does microcontroller can read the state of input signal if microcontroller running with 20Mhz crystal

 

hi,
In a PIC the crystal frequency is divided by 4, so a PIC with a 20MHz xtal is working at 5MHz.
So it cannot follow and read a 40MHz continuous input signal.
E

What is your application.?

 

For the PIC one instruction cycle time is 4 cycles of the crystal frequency. So one instruction cycle is 200 nS. So just to read a port into the W register will take 200 nS One bit of a 40 Mhz data stream is only 25 nS. Just getting a bit of data into one bit of the W register is only the first step in the process. You then have to do something with the data. (Maybe assemble 8 bits into a byte.) The only exception may be the Master Synchronous Serial Port when used with SPI data. You would need to study the data sheet to find the maximum speed for SPI data.

Les.

 

hi,
In a PIC the crystal frequency is divided by 4, so a PIC with a 20MHz xtal is working at 5MHz.
So it cannot follow and read a 40MHz continuous input signal.
E

What is your application.?

I had doubt only so I asked

My other doubt , Can I replace 20MHz crystal with 40MHz crystal ?

Will PIC16f877 run with 40Mhz crystal ?

 

It would not help if it could, so why are you asking?

Bob

 

No. Read the data sheet. It may help is you answer Eric's question in post #5. If we knew what you are trying to do we may be able to suggest a solution rather than just reading information from the data sheet for you.

Les.

 

You now ask for that specific micro but the next time you could resort to a different one that has PLL so with the same crystal it could run much faster. Keep that in mind. Typical of the 18F family.