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- New improved fail-safe detection and handeling for single or multible signal loss and receiver malfuntion
- Improved LED status for APM 2.x
- Improved jitter performance (PPM output using nested interrupts)

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ARDUPPM OPERATIONAL DESCRIPTION
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APM 2.x LED STATUS:
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RX - OFF         = No input signal detected
RX - SLOW TOGGLE = Input signal OK
RX - FAST TOGGLE = Invalid input signal(s) detected
RX - ON          = Input signal(s) lost during flight and fail-safe activated
TX - OFF         = PPM output disabled
TX - FAST TOGGLE = PPM output enabled
TX - SLOW TOGGLE = PPM pass-trough mode

SERVO INPUT (PWM) MODE:
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- PPM output will not be enabled unless a input signal has been detected and verified
- Verified inputs are lost during operaton (lose servo wire or receiver malfunction):
  + The PPM output channel for the lost input will be set to the default fail-safe value
  + PPM throttle output (ch3) will be permanently set to fail-safe (900us)
- Lost channel signal is restored:
  + PPM output for the restored channel will be updated with the valid signal
  + PPM throttle output (ch3) will not be restored, and will continue to output fail-safe (900us)

PPM PASS-THROUGH MODE (signal pin 2&3 shorted):
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- PPM output will not be enabled unless a input signal has been detected
- Active signal on input channel 1 has been detected:
  + Any input level changes will be passed directly to the PPM output (PPM pass-trough)
  + If no input level changes are detected withing 250ms:
    + PPM output is enabled and default fail-safe values for all eight channels transmitted
    + Input level change detected again, PPM fail-safe output is terminated and normal PPM pass-through operation is restored