UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

AR# 34845

FPGA - How do I place the GPIOs in tri-state until configuration is finished?

Description

How do I hold the user I/Os in tri-state until configuration is finished?

Solution

During configuration

A hot-swap pin named HSWAPEN controls the user I/O's state during the configuration process (the name of this control pin varies by device families: it is PUDC_B for Extended Spartan-3A, HSWAP for Spartan-3E, HSWAP_EN for Spartan-3, Virtex-II and Virtex-II Pro FPGA, and HSWAPEN for Virtex-4 and Virtex-5 FPGA). When this pin is High, the internal pull-up resistors on each user I/O are disabled and theI/O is in high-Z state during configuration.

HSWAPEN is active on the rising edge of INIT_B. This means that forsituations where PROG_B held low during power up theI/O aretristated until PROG is released and INIT subsequently is released High.

There is an exception for the Spartan-3 family. HSWAP pull-ups are enabled on the falling edge of PROG_B or when the POR threshold is crossed rather than on the rising edge of INIT.

Pre-Configuration Power-Up

Independent of the hot-swap pin, on power-on, user I/Os of most FPGAsare placed in tri-state until configuration starts. VCCINT VCCAUX VCCO is the "golden sequence" that will always guarantee tri-stated I/Os. There is an exception for Spartan-3 Generation devices which is documented in (Xilinx Answer 32653).

Linked Answer Records

Associated Answer Records

Answer Number Answer Title Version Found Version Resolved
39554 Spartan-6 - PUDC enabled Pullup timing N/A N/A
AR# 34845
Date Created 04/29/2010
Last Updated 01/23/2013
Status Active
Type General Article
Devices
  • Spartan-3
  • Spartan-3A
  • Spartan-3A DSP
  • More
  • Spartan-3AN
  • Spartan-3E
  • Virtex-4 FX
  • Virtex-4 LX
  • Virtex-4 SX
  • Virtex-5 FXT
  • Virtex-5 LX
  • Virtex-5 LXT
  • Virtex-5 SXT
  • Virtex-5 TXT
  • Virtex-II
  • Virtex-II Pro
  • Virtex-II Pro X
  • Spartan-6 LXT
  • Spartan-6 LX
  • Less