Bus Termination; Synchronization; D-Can - BMW i3 Technical Training Manual

I01￿General￿Vehicle￿Electronics
1.￿Vehicle￿Electrical￿System
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The￿FlexRay￿is￿shown￿in￿a￿simplified￿form￿in￿the￿overview￿of￿the￿bus￿systems.￿The￿FlexRay￿system
wiring￿diagram￿shows￿the￿actual￿physical￿layout￿(topology).
The￿FlexRay￿has￿a￿data￿transfer￿rate￿of￿10 MBit/s.
The￿control￿units￿at￿the￿FlexRay￿are:
• connected￿using￿an￿additional￿line￿at￿terminal￿15WUP
• or￿terminal￿15N.
FlexRay￿data￿bus￿topology￿for￿the￿I01
The￿star￿coupler￿with￿four￿drivers￿is￿located￿in￿the￿Body￿Domain￿Controller￿(BDC).￿The￿FlexRay￿control
units￿are￿connected￿to￿these￿bus￿drivers￿independent￿of￿their￿termination￿type.
Bus￿termination
As￿with￿most￿bus￿systems￿resistors￿are￿also￿used￿for￿termination￿for￿the￿FlexRay￿to￿avoid￿reflections
on￿the￿data￿lines￿at￿both￿ends￿of￿the￿data￿lines.￿The￿terminating￿resistors￿are￿located￿in￿the￿control
units.￿If￿only￿one￿control￿unit￿is￿connected￿at￿a￿bus￿driver,￿the￿connections￿at￿the￿bus￿driver￿and￿at￿the
control￿unit￿also￿have￿a￿terminating￿resistor.

Synchronization

In￿order￿to￿realize￿the￿synchronous￿design￿of￿individual￿functions￿in￿networked￿control￿units,￿a
common￿time￿base￿is￿required.￿As￿all￿control￿units￿work￿internally￿with￿their￿own￿clock￿generator,
the￿time￿synchronization￿must￿be￿done￿via￿the￿data￿bus.￿The￿control￿units￿measure￿the￿period￿of
certain￿synchronization￿bits,￿calculate￿the￿mean￿value￿and￿adapt￿their￿bus￿cycle￿to￿this￿value.￿The
synchronization￿bits￿are￿sent￿in￿the￿static￿part￿of￿the￿bus￿message.￿The￿synchronization￿starts￿in￿the
FlexRay￿after￿the￿system￿start￿between￿two￿control￿units￿that￿are￿authorised￿to￿perform￿wake-up
function￿(marked￿with￿"S"￿in￿the￿bus￿overview),￿once￿the￿Body￿Domain￿Controller￿has￿sent￿a￿wake-
up￿pulse.￿When￿this￿process￿is￿completed,￿the￿other￿control￿units￿log￿on￿at￿the￿FlexRay￿and￿calculate
their￿respective￿difference￿value.￿In￿addition,￿a￿mathematical￿correction￿of￿the￿synchronization￿is
done￿during￿operation.￿It￿is￿thus￿guaranteed￿that￿even￿the￿slightest￿time￿differences￿do￿not￿lead￿to
transmission￿errors￿over￿a￿longer￿period.
1.2.4.￿D-CAN
The￿D-CAN￿for￿the￿vehicle￿diagnosis￿has￿a￿data￿transfer￿rate￿of￿500￿kBit/s.
Explanation
Electronic￿Power￿Steering￿(EPS)
Dynamic￿Stability￿Control￿(DSC)
Body￿Domain￿Controller￿(BDC)
Optional￿equipment￿system￿(SAS)
Crash￿Safety￿Module￿(ACSM)
Electrical￿Digital￿Motor￿Electronics￿(EDME)
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