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AR# 9048

Virtex/-E/-II/-II Pro/-4/-5/-6, Spartan-II/-IIE/-3/-3A/-3AN/-6 - Which pins do not have clamp diodes?


When clamp diodes are enabled (based on the I/O Standard), which pins do not have the clamps? Do the JTAG pins have clamp diodes?


Virtex and Spartan-II

On these devices, all I/O standards have an intrinsic diode between the I/O pad and ground that limits undershoot to greater than -1 V. The LVCMOS 2.5V, LVTTL, and PCI 5V standards are all 5V-tolerant (both inputs and outputs) and do not have a pull-up clamp enabled. Because configuration pins default to LVTTL, these only have pull-down clamp diodes enabled.

Virtex-E and Spartan-IIE

These devices are provided with a pull-up clamp diode between the I/O pad and VCCO that allows them to be 5V-tolerant and reduces overshoot. The clamp diode is available with all I/O standards (including all configuration pins), excluding LVDS, LVPECL, GTL, GTL+, or LVCMOS1.8/2.5.

Virtex-II Pro Only

For Virtex-II Pro devices, all JTAG pins do not have clamp diodes, and the TDO is open drain. For more information, see the Virtex-II Pro/Virtex-II Pro X 3.3V I/O Design Guidelines Application Note(XAPP659).

Virtex-II/-II Pro/-4/-5/-6 and Spartan-3

For these devices, the following pins have pull-up and pull-down clamp diodes:

  • JTAG pins (except for Virtex-II Pro)
  • GCK0, GCK1, GCK2, GCK3
  • M0, M1, M2
  • CCLK
  • DONE
  • DXN, DXP (Temperature-sensing diode pins)

Note: VCCINT, VCCO, GND have a protection circuit, however,it might not be an explicit diode to Vcco and GND.

Spartan -3A/-3AN/-6

These devices have no pull-up diode clamps and use a floating n-well instead. For more information, see the Virtex-II Pro/Virtex-II Pro X 3.3V I/O Design Guidelines Application Note(XAPP659).

AR# 9048
Date Created 08/21/2007
Last Updated 03/11/2014
Status Active
Type General Article
  • Extended Spartan-3A
  • Spartan-3
  • Spartan-3A
  • More
  • Spartan-3A DSP
  • Spartan-3AN
  • Spartan-3E
  • Spartan-6
  • Spartan-6 LX
  • Spartan-6 LXT
  • Spartan-6Q
  • Virtex-4
  • Virtex-4 FX
  • Virtex-4 LX
  • Virtex-4 SX
  • Virtex-4Q
  • Virtex-4QV
  • Virtex-5
  • Virtex-5 FXT
  • Virtex-5 LX
  • Virtex-5 LXT
  • Virtex-5 SXT
  • Virtex-5 TXT
  • Virtex-5Q
  • Virtex-5QV
  • Virtex-6
  • Virtex-6 CXT
  • Virtex-6 HXT
  • Virtex-6 LX
  • Virtex-6 LXT
  • Virtex-6 SXT
  • Virtex-6Q
  • Virtex-6QL
  • Spartan-II
  • Spartan-IIE
  • Virtex
  • Virtex-E
  • Virtex-EM
  • Virtex-II
  • Virtex-II Pro
  • Virtex-II Pro X
  • Virtex QPro/R
  • Virtex-4 QPro/R
  • Virtex-E QPro
  • Virtex-II QPro/R
  • Spartan-3 XA
  • Spartan-IIE XA
  • Less