SpaceWire Avionics Data Bus

SpaceWire Description

The SpaceWire interface is a Point-to-Point cable bus used to handle payload data on-board a spacecraft.
The SpaceWire specification defines the Physical, Electrical and Protocol layers of the interface.
SpaceWire operates from 2Mbps to 400Mbps over a full-duplex point-to-point serial link over a distance of 10m.
The SpaceWire interface is defined by the following organizations:
IEEE 1355.2: SpaceWire, based on the HIC (IEEE-1355) bus, and Low Voltage Differential Signaling (EIA-644).
SpaceWire is also controlled by the European Space Agency, for the ECSS [European Cooperation for Space Standardization].
ECSS-E-50-12 Defines the Mechanical, Electrical, and Protocol. At data rate of 100Mbaud (min.) over a distance of 10 meters.

SpaceWire Standard

IEEE 1355.2: SpaceWire protocol, derived from
SpaceWire Serial Point-to-Point Links ECSS-E-50-12; Draft Issue C
SpaceWire Links, Nodes, Routers and Networks ECSS-E-50-12; Draft Issue 2
IEEE: Institute of Electrical and Electronic Engineers []
esa: European Space Agency []

SpaceWire Electrical Description

SpaceWire uses LVDS, +/- 247mV to +/- 454mV.
SpaceWire uses 'Data-Strobe' (DS) Encoding, at a minimum data rate of 2Mbps (before timing out).
Normal data rates after 'start-up' are 100Mbps and 200Mbps. Modules initially operate at 10Mbps after a reset.

SpaceWire physical layer transceiver
Spacewire Physical Layer Transceiver

5962-06232; Microcircuit, Digital, Radiation Hardened, Spacewire Physical Layer Transceiver, Monolithic Silicon
UT200SpWPHY01; SpaceWire physical layer transceiver [Flat pack]
UT200SpWPHY01; SpaceWire physical layer transceiver, extended industrial temperature range

SpaceWire Signaling Description

SpaceWire Data is sent in characters which are formed by a 'Parity bit', 'Data-Control Flag', and 8 data bits {LSB to MSB}. SpaceWire uses Odd Parity, the Data Control Bit is low to indicate data. Control words are sent with only 2 data bits. SpaceWire uses 'Data-Strobe' (DS) Encoding. The strobe changes when the data remains constant between bit intervals ~ the clock may be recovered by XORing the Data and Strobe lines (also used by IEEE-1355, and IEEE-1394).

Spacewire Strobe Clocking Implementation
Spacewire Timing

Control characters are sent with three bits preceded with a Parity bit. Time code characters are longer.
Flow Control Token; FCT: P100
Normal End of Packet; EOP: P101
Error End of Packet; EEP: P110
Escape; ESC: P111
Null; P1110100, {ESC / FCT} also sent to avoid a link disconnect
After 850nS the link is considered disconnected if no bits are received.

SpaceWire Connector/Cable Description

The cable used with SpaceWire consists of 4 Shielded Twisted Pairs (STP), with a differential impedance of 100 ohms, surrounded by another shield. The cable terminates on a 9-pin D connector, pinout below. The individual wires are 28 wire gauge [7 x 36 AWG stranded wire]. The entire wire bundle is 40AWG. The conductors are silver coated. The cable end uses a Plug, while the equipment side uses a socket. Din/Sin is connected to Dout/Sout on the far end.
Refer to the link for 9-pin Dsub connector manufacturers. The micro-miniature D-type connector must be qualified for space use.
Each differential signal pair is defined to have a skew of no more than 0.1nsec/m.

9-Pin D connector

DB-9 Connector Pin Out
Pin Signal name Description
1 DIN+ Data In
2 SIN+ Strobe In
3 Inner Shield Ground
4 SOUT- Strobe Out
5 DOUT- Data Out
6 DIN- Data In
7 SIN- Strobe In
8 SOUT+ Strobe Out
9 DOUT+ Data Out

Dsub Connector Dimensions [Shell size]
Dsub Connector Insert Arrangement [Pin spacing]
Note that IEEE1355 uses a different D connector than SpaceWire.
Although the connector is still D-shaped, it is not a 9-pin D connector.
The IEEE1355 connector may also not be qualified for usage in space.

SpaceWire physical IC, Flat Pack
Spacewire IC

PC motherboard

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Modified 1/16/12
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