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SpaceWire Frequently Asked Questions

This page shows the answers to frequently asked questions regarding SpaceWire.

1. How does SpaceWire differ from the original IEEE-1355 standard?

SpaceWire is an upgrade for space of the DS-DE (DataStrobe-Differential Ended) part IEEE 1355-1995 Standard (also ISO/IEC 14575) Heterogeneous InterConnect (HIC), which includes several high-speed point-to-point communication sub-standards.

The main differences between the the original IEEE 1355 and SpaceWire are summarised below and explained in more detail in Annex A of the SpaceWire Standard.

  • 9-way micro-miniature D-type connectors instead of the original 10 pin connectors.
  • New four-twisted-pair shielded cables.
  • LVDS (Low Voltage Differential Signaling) transceivers instead of the original PECL. LVDS is defined in two standards:
    • TIA/EIA-644, on which SpaceWire is mainly based, and
    • IEEE 1596.3, which includes additional specifications for SCI interfaces.
  • LVDS transceivers offer, with respect to the original PECL transceivers in the IEEE 1355 Standard:
    • lower power consumption,
    • better EMC performance.
  • Slightly modified character level.
  • Robust STATE-DIAGRAM at the exchange level to support warm-plug capabilities.
  • Network level specified for the first time in SpaceWire DRAFT-D.
  • Additional recommendations in the protocol level to support fault-tolerance and recovery schemes.
  • Time-distribution was not foreseen in IEEE 1355 and is included in SpaceWire.

In addition, SpaceWire is the result of extensive simulations that have enabled the correction of many of the inconsistencies within the original IEEE 1355-1995 Standard.

Note: The SMCS devices implement revision A of the standard, which is based on IEEE1355. They do not implement the current version of SpaceWire. However, the current version of SpaceWire is backwards compatible with the earlier revision.

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