Robert F. Hodson, NASA LaRC

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Actel Compact PCI Signal Integrityfor RTSXS
SXA devices

• Robert F. Hodson, NASA LaRC
• Kevin Somervill, NASA LaRC
• Mark Jones, NASA LaRC
• Guy Gibson, Northrop Grumman

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Initial simulations

These initial simulation performed by Northrop
Grumman raised questions and concerns that
prompted this study.
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Actel Datasheet info (continued)
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Datasheet info (continued)
What about 3.3V operation?
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Datasheet info (continued)
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Datasheet info (continued)
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PCI Specifications

• PCI and Compact PCI designed for commercial
  systems
• Puts the onus on manufacturers to tolerate a
  broad range of operating conditions
• The following should be use to evaluate long term
  device reliability

Appears to contradict the maximum ratings of
Actels devices
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cPCI Driver Simulations

• The following slides show HyperLynx simulations
  performed at NASA LaRC to simulate an Actel
  device (in slot 3) driving another Actel device
  (in slot 7).
• 3.3V PCI I/O is used
• 20 degrees C
• The simulation is done for both the RTSXS devices
  and SXA commercial devices
• Simulations with Spartan and Vertex II IBIS
  models are also shown for comparison.

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HyperLynx Schematic
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RTSXS Model slot 3 driving slot 7
Note datasheet maximums exceeded
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Non-monotonic signal in transition region
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Sxacom Model slot 3 driving slot 7
Note datasheet maximums exceeded
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Spartan model slot 3 driving slot 7
Note similar undershoot, cleaner signal.
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Vertex II slot 3 driving slot 7
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Lab Test Setup

• Actel source board (Actel 3.3V PCI I/O) in slot 3
• A54SX32A device with Actel PCI core
• Actel destination board (Actel 3.3V PCI I/O) in
  slot 7
• A54SX32A device with Actel PCI core
• Commercial PCI bus
• Commercial processor board in slot 1
• 33 MHz operation

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Data line showing under/overshhoot
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Non-Monotonic signal at receiver
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Actel Responses 8/18/04

• Actel has performed experiments on the PCI clamp
  diodes of the RTSXS device.
• In the 3.3V PCI configuration, the Power Clamp
  diode effectively clamps any incoming voltage (up
  to 7.1V) to about 4.6V. This is within Actels
  maximum rating (5.75V).
• The Ground Clamp diode clamps any incoming
  undershoot (up to -3.5V) to 1.2V. This clamped
  voltage is outside the maximum rating specified
  by Actel (-0.5V)
• PCI Reliability (260 hour stress test)
• Actel is performing a reliability experiment on
  the RTSXS IO buffer in the PCI configuration to
  test the effect of input voltage excursions
  outside the normal operating rage. In this
  experiment the RTSXS device with the IO buffers
  configured as 3.3V PCI inputs are stressed
  continuously to a switching signal that conforms
  to PCI requirements (VIH7.1V and VIL-3.5V with
  a pulse width of 11ns each). Preliminary pre and
  post stress measurements were taken for Leakage
  and VIH/VIL. The maximum IIL/IIH delta was of the
  order of a few nanoamps and maximum VIH/VIL delta
  of about 50mV.
• Based on the reliability results so far, we dont
  believe there is any issue with input voltages
  switching beyond the rails, as long as it is
  within PCI specifications. Upon completion of the
  reliability testing the datasheet will be
  updated.
• The experiment was done on a MEC device. The same
  experiment is being repeated on a UMC device
  (RTSX-SU).

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Summary

• There appear to be inconsistencies between the
  Actel data sheets and the PCI specification
• Overshoot and undershoot in the simulations and
  the lab appear to exceed maximum rating for Actel
  3.3V PCI I/O
• Non-monotonic behavior observed in simulations
  and the lab. Did not affect operation in this
  single test case, effect on other vendor devices
  unknown.
• Initial Actel over/undershoot testing has not
  uncovered reliability issues with PCI
• Actel plans to continue testing and update data
  sheets