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sending data from 50 MHz to 100Mhz

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boopathy13

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Hi friends,

I have a question realted to CDC.

if i transmit a enable signal from 50Mhz to 100Mhz, then one enable signal becomes 2 enable signal in the 100Mhz region.
which means the module which is working in 100Mhz will think like it will get 2 times trigger from 50Mhz.

Can you please explain hoe to solve this?
 

sivamani

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is it edge triggered or Level triggered?
It will change only duration of the pulse not count..
 

boopathy13

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Hi sivamani,

It is edge triggered.

let me explain it in more clear.
if one trigger comes from 50Mhz to 100Mhz, while reading the same trigger in 100Mhz it may think that it has received two times the trigger. so process will be initiated two times.
How to overcome this problem?
 

Venkadesh_M

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use a T flip flop as frequency divider to get the correct frequency.or If you need to operate in 100MHz give clear system diagrams..
 

boopathy13

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Hi vengatesh,

My problem is different.

I have two modules, first one is in 50 MHz, 2nd one is in 100Mhz.
i am sending one ctrl signal from 50Mhz module to 100Mhz module. that is high for one clock period of 50 MHz. If you sample tat ctrl signal in 100Mhz module that signal will be high for two clock period of 100MHz.
So if its high for two clock period, it may cause some other problem.

How to overcome this problem.

Note:- i couldnt able to add image file here.
 

Venkadesh_M

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You can attach a jpg or png image by clicking insert image icon in reply box...

It is difficult to say whether a signal from 50MHZ will match in 100MHz or not because its fully depends on what protocol you are using or what kind of control signal you are talking about so for a exact answer need more detail about the signal....
 

boopathy13

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Hi

I am not using any protocol. simply am sending one signal from one module to another module.
 

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Venkadesh_M

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Hi nothing will be a problem in this interface but there will be no use of 100MHZ side...
But if you interchange the modules like 100Mhz to 50 MHz you will lose half the data and that wont work..
 
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imbichie

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Hi Boopathy,

Whether the 50MHz clock and the 100MHz are synchronous clock or asynchronous?
If they are asynchronous, then you should follow any of the CDC design, like DMUX/MUX synchronization mechanism or Double flopping mechanism.
If they are synchronous, then you can make a select/control signal from the 100MHz clock, means create a signal say "sig_100_by_2",
then on reset make it low, then toggle the signal in 100MHz clock. So you will get a signal which is in 100MHz domain but its frequency will be 50MHz,
then you can use this "sig_100_by_2" signal through out your 100MHz domain, means once the "sig_100_by_2" is high then you can performs the operations you want
and if the "sig_100_by_2" is low you can do nothing.
 

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boopathy13

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Dear Shibin Bose Kavara,

Really thank you very much. I got my answer.
I have been searching for this answer for long time.
 

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