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Newbie aperez_121
Newbie
218 Views
Registered: ‎06-04-2019

Having trouble getting Artix-7 won't drive 1.8V

Hello everyone,

I'm a newbie at FPGA and Vivado, and I'm trying to get my outputs to drive 1.8V. I am using the Artix-7. In Vivado under Implemented Design, in the Package Pins window, I have set my pins to LVCMOS18, however when I measure the outputs, I get a voltage level of 3.3V. Is there a way to make the output 1.8V or an I misunderstanding something? Thanks.

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2 Replies
Xilinx Employee
Xilinx Employee
188 Views
Registered: ‎06-21-2018

Re: Having trouble getting Artix-7 won't drive 1.8V

Hi aperez,

You need to check which is the power supply to that Bank.

Which Evaluation Board are you using and which pins are you trying to use with LVCMOS18?

Thanks,
Andres

 

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Historian
Historian
177 Views
Registered: ‎01-23-2009

Re: Having trouble getting Artix-7 won't drive 1.8V

All the single ended I/O standards drive their outputs "to the rail" - to the voltage applied to the I/O bank of the pin. This is the "VCCO" of the bank. All I/O are part of a bank, which contains a constant number of pins (in the 7 series this is 52 I/O per bank), and all the pins within the bank share the same VCCO.

You are only supposed to use an I/O standard that is compatible with the VCCO of the bank. So using an LVCMOS18 I/O standard in a bank with VCCO=3.3 is "illegal". However, the tools have no mechanism of determining the actual bank voltage, so can't check if the I/O standard you are using is compatible with the actual VCCO voltage on the board - they can merely look for consistency. For example, if you try and place a LVCMOS33 and an LVCMOS18 I/O in the same bank, the tool will issue an error (and not generate a bitstream).

But, presumably, you placed only LVCMOS18 I/O in a bank with VCCO=3.3. The tools did not complain since they did not know about the VCCO, and hence generated a bitstream. The net result is that even though you specified an I/O standard of LVCMOS18, with the VCCO=3.3, the I/O behaves like a 3.3V I/O (with somewhat non-standard characteristics since the I/O is misconfigured).

And, as a direct answer to your question "no" - the I/O levels of an output are determined by the VCCO - regardless of what I/O standard you use you will only be able to get a 3.3V I/O out of a bank with VCCO=1.8. If you need a 1.8V I/O you must use a bank that has a VCCO=1.8V.

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