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AR# 59958

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

Description

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.

Solution

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 03/25/2014
Last Updated 05/22/2014
Status Active
Type General Article
Devices
  • XA Zynq-7000
  • Zynq-7000
  • Zynq-7000Q
  • More
  • Artix-7
  • Artix-7Q
  • Kintex-7
  • Kintex-7Q
  • Virtex-7
  • Virtex-7 HT
  • Virtex-7Q
  • Less