Hi, RobertJ.
I'm reading the spec of PIC MCU(micro controller). The device is 16F1824.
In section 5.4 "Two-Speed Clock Start-up Mode"
There are full content in section 5.4:
Two-Speed Start-up mode provides additional power savings by minimizing the latency between external oscillator start-up and code execution. In applications that make heavy use of the Sleep mode, Two-Speed Start-up will remove the external oscillator start-up time from the time spent awake and can reduce the overall power consumption of the device. This mode allows the application to wake-up from Sleep, perform a few instructions using the INTOSC internal oscillator block as the clock source and go back to Sleep without waiting for the external oscillator to become stable.
Two-Speed Start-up provides benefits when the oscillator module is configured for LP, XT, or HS modes. The Oscillator Start-up Timer (OST) is enabled for these modes and must count 1024 oscillations before the oscillator can be used as the system clock source.
If the oscillator module is configured for any mode other than LP, XT or HS mode, then Two-Speed Start-up is disabled. This is because the external clock oscillator does not require any stabilization time after POR or an exit from Sleep.
If the OST count reaches 1024 before the device enters Sleep mode, the OSTS bit of the OSCSTAT register is set and program execution switches to the external oscillator. However, the system may never operate from the external oscillator if the time spent awake is very short.
Sorry that I didn't come up with a good idea for letting you know the situation of me but only pasted the full content.
BTW, may I ask you an other question that in this sentence "When your car passes over the sensor it (the sensor) sends a signal to the traffic light." . Why there is no comma between sensor and it? Isn't that two independent clause?
