Regarding Spartan III interface

[preet]

hello all,

i want to interface FPGA I/O to 5V TTL level or 5V devices so what should i do to make it 5V tolerant.

Regards

Preet

 

[IanP]

You can use level shifters similar to these in the attached files:
**broken link removed**
http://www1.idt.com/pcms/tempDocs/74ALVC164245_datasheet.pdf

 

[preet]

hello sir,

then at Board level the design get to much complicated, due to more I/O pins

 

[IanP]

If you want to transmitt from 3.3V logic to 5V TTL you will be OK.
See attached info on logic levels:
https://www.allaboutcircuits.com/vol_4/chpt_3/11.html
Transmission from TTL: may generate levels close to 5V and in this case you may damage low-voltage inputs ..

 

[preet]

Thanks sir

But could i connect Resistor i series to limit the current

 

[IanP]

It can be a resistor but you will have to limit the voltage to ≤3.3 using a zener diode (not for very fast applications) or 4 fast diodes in series and keep in mind input current requirements (for L logic) for TTLs inputs ..