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Spartan 3 Xilinx IO Standards

Can anyone point me to a tutorial or explanation of the IO standards? And how to set the default? Seems as if the synthesis tool has assigned LVCMOS25 as the default setting although I don't recall setting this standard. As my IOs for my design are entirely 3.3V, shouldn't my default be LVCMOS33?

Additionally in the PACE windows under Design Object List there is a section with Groups listed. Not sure what this is for, however, I have a group listed with no ( # 0) items in the group for a symbol I recall that I deleted from the VHDL code a long time ago. How do I get rid of this old group?

Thanks,

Brad

Reply to
Brad Smallridge
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Hi,

Select any pin under "Design Object List - I/O Pin" window in PACE and then right-click. You'd then get an option to set the I/O standard for that pin.

You can do the same by selecting multiple signals.

Narasimha.

Reply to
Narasimha

Hi,

Refer to....

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It gives a fairly good introduction to different I/O standards.

Narasimha.

Reply to
Narasimha

Thanks for the article, Narasimha.

Still need information about (or if possible) to set the default IO standard, getting rid of an old group, and it just occured to me that I am assuming that the 33 after LVCMOS refers to the Vcco but I never confirmed that. Might it be something else like the Voh?

Brad

And

LVCMOS25

As my

section

old

Reply to
Brad Smallridge

Brad,

These FPGA vendors never make our life simpler. LVCMOS33 is supposed to refer to 3.3V LVCMOS I/O Standard. I too am a little confused on this. Recently, on a Lattice CPLD I was using, the tool selected the default i/o standard as lvcmos18. I generated the jed file and tested and everything was running cool. Only later did I realise that i selected 1.8v io standard on the cpld whereas all the ios on my board are 3.3v :( I think the cpld didnt burn because it requires a VCCIO and that is 3.3V....

I know how to set the default io standard option in Lattice constraints file. For xilinx.... will let ya know when I know it myself.

Narasimha.

Reply to
Narasimha

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