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Registered: ‎05-27-2019

Pulldown

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Hello,

I'm using a Zybo Board with Vivado 2018.3 and I'm trying to change a J-Port pin from input to pulldown but it won't work.

While searching on Google I found this thread https://forums.xilinx.com/t5/Welcome-Join/Use-PULLDOWN-on-input-pin/m-p/643544#M29708 but I could not make it work for me.

To test it I made a very simple IP with only two inputs (DataIN and clk) and not outputs.

DataIN is connected to Pin 1 from the JA port. To test the code I connected a LED between the 3,3V pin and the DataIN pin.

If the pin is set to pulldown the LED should be on. In my case the LEDs stays off.

Beside implementing the library and setting up the ports (DataIN, clk) and the signal (temp_data) this is pretty much my whole code.

 

PULLDOWN_inst : PULLDOWN 
port map( 
O => temp_data
);
	
	-- Add user logic here
	a: process (clk) begin
	    temp_data <= DataIN;
	end process;

	-- User logic ends

The constraint:

 

set_property -dict { PACKAGE_PIN N15   IOSTANDARD LVCMOS33 } [get_ports DataIN_0]; 

grafik.png

I would be glad for any hints how to make it work.

Best regards

tklaas

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214 Views
Registered: ‎06-21-2017

Re: Pulldown

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The pull down does not appear on the schematic.  Since DataIn does not affect any output of yur FPGA, it is optimized away.

View solution in original post

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Registered: ‎06-21-2017

Re: Pulldown

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I don't have the exact numbers, but an internal pull-down on an FPGA pin is on the order of 10KOhms or so.  It will not sink enough current to light an LED.  Typically a current limiting resistor for an LED is on the order of a couple hundred ohms.

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Visitor
Visitor
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Registered: ‎05-27-2019

Re: Pulldown

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Thanks for the answer, I will take this in mind for further tests.

But I checked the schematic from the RTL analysis and the DataIN port is going to nowhere instead to the pulldown.

grafik.png

 

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Registered: ‎06-21-2017

Re: Pulldown

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The pull down does not appear on the schematic.  Since DataIn does not affect any output of yur FPGA, it is optimized away.

View solution in original post