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Newbie onidaito
Newbie
189 Views
Registered: ‎06-05-2019

VREF on Spartan 7

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Hello there,

I'm wondering what to do with my VREF pins on the Spartan 7? I've looked at the documentation and I can't figure out. Why? Because I'm using 3.3v on my I/O lines. Now I'd have thought that VREF should match 3.3v - a reference for the I/O. This seems to be the case for the Spartan 7 BUT there is a problem. The maximum setting for VREF on this chip is 2.0V. Now I saw somewhere that we set VREF to half of what our I/O line is (which would be 1.7666 or so - probably 1.8v). However, the spartan7 appears to have an INTERNAL VREF so do I even need to bother with this pin at all?

I should stress this design is an initial test that simply turns on and off an LED. I'm progamming with the xilinx JTAG interface so I'm doing nothing complicated or demanding.

Should I link VREF to 1.8v or should I just leave all these VREF pins unconnected?

Cheers

Ben

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Highlighted
176 Views
Registered: ‎09-17-2018

Re: VREF on Spartan 7

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b,

Vref is only used for those IO standards which require it.  So, if needed, the standard tells you its voltage to use (see SSTL, HSTL, etc.).

Otherwise, they are unused.

l.e.o.

 

2 Replies
Highlighted
177 Views
Registered: ‎09-17-2018

Re: VREF on Spartan 7

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b,

Vref is only used for those IO standards which require it.  So, if needed, the standard tells you its voltage to use (see SSTL, HSTL, etc.).

Otherwise, they are unused.

l.e.o.

 

Newbie onidaito
Newbie
159 Views
Registered: ‎06-05-2019

Re: VREF on Spartan 7

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Marvellous! Thank-you. I suspect I don't need it, so I'll leave it unconnected for now, though I'll double check the JTAG programming guide just to be sure.

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