| 摘要 |
The communication bus system comprises a plurality of node circuits ( 10 a-d) and a relay circuit ( 12, 14, 16 ) coupling the node circuits ( 10 a-d). The relay circuit ( 12, 14, 16 ) has a transceiver circuit ( 124, 164 ) for relaying messages ( 21 ) between the node circuits ( 10 a-d) in a normal mode. The transceiver circuit ( 124, 164 ) is powered down in a sleep mode. A detector circuit ( 120, 160 ) detects an incoming message ( 41 ) when the relay circuit ( 12, 14, 16 ) is in a sleep mode. A mode control circuit ( 122, 162 ) powers up the transceiver ( 124, 164 ) in response to detection of an incoming message ( 21 ). Steps are taken that ensure, in the normal mode, that messages ( 21 ) will not be relayed in unreadable form. The mode control circuit ( 122, 162 ) is arranged to cause the transceiver ( 124, 164 ) to relay a remainder ( 25 ) of the incoming message ( 21 ) after power up. In an embodiment the power needed to transmit the remainder ( 25 ) of the message ( 21 ) is drained from a capacitor ( 306 ) in the power supply ( 30 ) before the power supply ( 30 ) controls the power supply voltage in the normal mode. In another embodiment the detector circuit ( 120, 160 ) temporarily controls the direction of operation of the transceivers ( 124, 164 ) at the start of the normal mode instead of further detectors ( 58 a-d) that normally control the direction of operation in the normal mode.
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