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1,405 Views
Registered: ‎12-07-2016

Using IOBUF for load detection

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Hello,

 

I have a FPGA board with a number of connectors for custom boards.

Now I want to implement the feature whether a board is connected or not. Unfortunately I don't have a dedicated signal for this.

 

But there is a reset signal on the boards which has a pullup resistor.

My question is now, can I use a IOBUF to "read" the state of this signal?

--> Board connected: Signal is high through pullup

--> Board disconnected: Signal is low

 

Thanks.

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austin
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1,820 Views
Registered: ‎02-27-2008

Yes,

 

You should place a weak pulldown on the board doing the sensing, I would use ~ 10x the resistance of the pullup as the pulldown.  Also, be sure not to enable the built in pullup.

Austin Lesea
Principal Engineer
Xilinx San Jose

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austin
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Scholar
1,821 Views
Registered: ‎02-27-2008

Yes,

 

You should place a weak pulldown on the board doing the sensing, I would use ~ 10x the resistance of the pullup as the pulldown.  Also, be sure not to enable the built in pullup.

Austin Lesea
Principal Engineer
Xilinx San Jose

View solution in original post

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1,343 Views
Registered: ‎12-07-2016

Hello,

 

thanks for the replay. I will try it...

Can I use the built in pulldown of the FPGA? 

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austin
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1,326 Views
Registered: ‎02-27-2008

a,

 

The internal pullup and pulldown vary with process corner +/- 40% (see data sheet) or so.  Best to use known resistance values.

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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