Yamaha YX600S Service Manual page 319

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DIGITAL IGNITION CONTRL SYSTEM
DESCRIPTION
The electronic ignition that sparks the engine is
computer controlled and operated by the digital
microprocessor. It has a pre-programed ignition
advance curve.
This programed advance curve closely matches
the spark timing to the engine's ignition require-
ments. Only one pickup coil is needed to meet
the requirements of the digital ignitor unit.
The digital ignitor also includes the control
unit for the electric fuel pump.
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[Al
Pickup coil
ffil
Wave-shape shaping circuit
[CJ
Edge detection circuit
[QJ
Latch circuit
[EJ
Microprocessor
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Free-running counter
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Comparison circuit
[8]
Register
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Flip-flop circuit
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Driving circuit
IBJ
Ignition coil
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Digital ignitor unit
OPERATION
The following operations are digitally-performed
by signal from the pickup coil.signal:
1. Determing proper ignition timing.
2. Sensing the engine revolution speed.
3. Determing timing for switching on ignition
coil (duty control).
4. Increasing ignition coil primary current for
starting the engine.
5. Sensing engine stall.
6. Preventing over-revolution of the engine.