NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

GROUND THE MODE PIN

NOW!!!!!!!!!!!!!!!!!!!!!

Termination of MODE Pins in Actel Field Programmable Gate Arrays1

The MODE pin is used in some models of Actel Field Programmable Gate Arrays to enable switching of the device between operational, programming, and test modes2. Improper termination of this pin along with the other special-purpose pins has occurred on multiple NASA programs. If the MODE pin is not correctly asserted, an indeterminate number of things can occur (e.g., transistors sinking large currents).

  1. Ground Operations: Devices that have been powered without the MODE pin grounded3 at any time are potentially overstressed. Actel will not guarantee the long-term reliability of parts that have been operated under these conditions.
  2. Spaceflight Operations: The MODE pin must be connected to circuit ground to guarantee proper operation of the device. Any other termination (floating or tied high) may result in either failure and/or damage.
  3. Failure to properly terminate the MODE pin on NASA circuit boards has resulted in malfunctions, dependent on a variety of conditions (e.g., power supply rise time characteristics).

 

Notes

  1. There is no MODE pin in Actel RT54SX and RT54SX-S series devices. See "Use of SX Series Devices and IEEE 1149.1 JTAG Circuitry" for additional information.
  2. When asserted low, the MODE pin forces the internal configuration register into the operational state. There is no internal power-on reset provided in the device to initialize these register bits.
  3. [and without properly controlling the contents of the configuration shift register.]

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Last Revised: November 04, 2004
Digital Engineering Institute
Web Grunt: Richard Katz
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