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AR# 63950

7 Series Config - I/Os may appear to have a weak pull-up enabled between the assertion of PROG_B, and when PUDC is sampled on the falling edge of INIT_B. Can I keep the value of PUDC during this period?

Description

In 7 series devices, PUDC dictates the state of the I/Os during configuration. 

Regardless of the value of PUDC, if PROG_B is asserted on a configured device, a pull-up may appear on the line of all I/O until just after PUDC is sampled on the falling edge of INIT_B (~100ns). 
 
Why is there a pull-up present during reconfiguration? 

Can I turn it off?

Solution

On a configured device, PUDC is sampled on the falling edge of INIT_B. 

The use of PUDC in the user design determines if a PULLUP on all I/O is present prior to INIT_B assertion.

  • If the PUDC pin is used in the current design - The presence of a weak PULLUP on all I/O will be dictated by the level seen on the PUDC pin.  (Logic HIGH - NO PULLUP, Logic LOW - PULLUP)
  • If the PUDC pin is not used in the current design (i.e. it is an unused pin) -  The weak PULLUP will always be enabled between PROG_B assertion and just after INIT_B asserts.

If the state of the I/O is relevant on a design that is being reconfigured, using the PUDC pin as an input can ensure that the value seen on PUDC dictates the presence of a pull-up between the assertion of PROG_B and INIT_B.  
AR# 63950
Date Created 03/18/2015
Last Updated 05/18/2015
Status Active
Type General Article
Devices
  • Virtex-7
  • Artix-7
  • Kintex-7