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Visitor byzantinus
Visitor
3,154 Views
Registered: ‎06-13-2014

unprogrammed FPGA I/O electrical behavior

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Hello,

 

Where can I find the electric description (AC impedance, DC current) of the user I/O pins of an unprogrammed V7? (I guess the question can be extended to other FPGAs as well).

Let's imagine the following scenario: a source block supplies through an N-bit bus a signal that is fed into the I/O pins of such an unprogrammed FPGA (of course those pins, after programming, will turn into input pins and the FPGA will perform a certain function on the incoming data, before passing it on); let's imagine the source block outputs to be LVCMOS18 and Z0=50ohm (and the FPGA inputs, once programmed, will match that). What will the behavior of the unprogrammed FPGA pins be (AC impedance, DC current), i.e., what will the source block see, before the FPGA gets programmed? I mean, before FPGA programming even begins.

 

Regards,

 

Paul

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Xilinx Employee
Xilinx Employee
4,229 Views
Registered: ‎10-11-2007

Re: unprogrammed FPGA I/O electrical behavior

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......And PUDC_B is high such that the weak pullups are not enabled. As a side note, after all supplies are up then the I/Os are tri-stated. If you need them to be tri-stated during power on then please follow the recommended sequence in the datasheet.

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3 Replies
Xilinx Employee
Xilinx Employee
3,149 Views
Registered: ‎07-23-2012

Re: unprogrammed FPGA I/O electrical behavior

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Hi Paul,

If you have followed the power on sequence, then the I/Os would be in tri-state before configuration of the device.

Regards,
Krishna
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Xilinx Employee
Xilinx Employee
4,230 Views
Registered: ‎10-11-2007

Re: unprogrammed FPGA I/O electrical behavior

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......And PUDC_B is high such that the weak pullups are not enabled. As a side note, after all supplies are up then the I/Os are tri-stated. If you need them to be tri-stated during power on then please follow the recommended sequence in the datasheet.

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Visitor byzantinus
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3,127 Views
Registered: ‎06-13-2014

Re: unprogrammed FPGA I/O electrical behavior

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Thanks both to Krishna and to ralfk for the complementary answers.

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