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Valued Contributor III
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cmos vs ttl logic in schematics design

Hi, 

I am designing cyclone 3 FPGA board in which i have come across cmos logic circuit and ttl logic circuit.  

can i connect 3.3v of both the cmos and ttl logic? 

what are all the things we have to taken care when go for different logics? 

Thanx in advance :) 

 

Regards, 

Shahul
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Valued Contributor III
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--- Quote Start ---  

Hi, 

what are all the things we have to taken care when go for different logics? 

Shahul 

--- Quote End ---  

 

http://focus.ti.com/lit/sg/sdyu001z/sdyu001z.pdf 

page 9.
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Valued Contributor III
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A 3.3V I/O standard can drive LVTTL, LVCMOS(both 3.3V supply) and TTL (5V supply). To drive 5V CMOS (e.g. 74HC family), you need a level converter. 74HCT logic has TTL levels on input and can be driven by the 3.3V I/O. 

 

5V logic must not drive the FPGA without level conversion or voltage clamping.
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Valued Contributor III
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thanx for ur reply 

It will be useful. 

 

Regards, 

shahul
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