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AR# 59958

7 Series and Zynq-7000 devices: what happens if PUDC_B is left floating?


The Configuration User Guide for 7 Series devices (UG470) states that the PUDC_B signal must be pulled high or low external to the device in order to have the optional internal pull-up resistors on the SelectIO pins present prior to Configuration completing.

The User Guide does not state what will happen if this pin is left floating.


UG865 and UG475 both have a pin description for PUDC_B that warns "CAUTION! Do not allow this pin to float before and during configuration."  

If PUDC_B in 7 series or Zynq devices is left floating on the board, the behavior of the SelectIO pins will be unknown.

It is possible it will be pulled up, or 3-stated, or in the worse-case, toggling might occur (from noise on the PUDC_B pin causing it to float above or below the input threshold). 
AR# 59958
Date Created 09/04/2007
Last Updated 05/22/2014
Status Active
Type General Article
  • XA Zynq-7000
  • Zynq-7000
  • Zynq-7000Q
  • More
  • Artix-7
  • Artix-7Q
  • Kintex-7
  • Kintex-7Q
  • Virtex-7
  • Virtex-7 HT
  • Virtex-7Q
  • Less