Specifications

mikroElektronika | Free Online Book | PIC Microcontrollers | Chapter 8: Other MCU's Circuits
Fig. 8-13 Internal Oscillator settings
2. The low-frequency oscillator LFINTOSC is uncalibrated and operates at 31 kHz. It is enabled by selecting this frequency
(bits of the OSCCON register) and setting the SCS bit of the same register.
Two-Speed Clock Start-up Mode
Two-Speed Clock Start-up mode is used to provide additional power savings when the microcontroller operates in sleep
mode. What is this all about?
When configured to operate in LP, XT or HS modes, the external oscillator will be switched off on transition to sleep in
order to reduce the overall power consumption of the device.
When conditions for wake-up are met, the microcontroller will not immediately start operating because it has to wait for
clock signal frequency to become stable. Such delay lasts for exactly 1024 pulses. After that, the microcontroller proceeds
with program execution. The problem is that very often only a few instructions are performed before the microcontroller
is set up to Sleep mode again. It means that most of time as well as power obtained from batteries is wasted. This
problem is solved by using internal oscillator for program execution while these 1024 pulses are counted. Afterwards, as
soon as the external oscillator frequency becomes stable, it will automatically take over the “leading role”. The whole
process is enabled by setting one bit of the configuration word. In order to program the microcontroller it is necessary to
select the Int-Ext Switchover option in software.
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