For this case, the OST is not necessary after a wake-up from Sleep, since Timer1 continues to run during Sleep and uses the same LP oscillator circuit as its clock source to Read Out Secured PIC16C63A Microcontroller. For these devices, this case is typically seen when the LCD module is running during Sleep.
In applications where the OSCTUNE register is used to shift the FINTOSC frequency, the application should not expect the FINTOSC frequency to stabilize immediately.
In this case, the frequency may shift gradually toward the new value. The time for this frequency shift is less In order to minimize latency between external oscillator start-up and code execution, the Two-Speed Clock Start-up mode can be selected (see Section 4.6 “Two-Speed Clock Start-up Mode”).
The External Clock (EC) mode allows an externally generated logic level as the system clock source. When operating in this mode, an external clock source is connected to the OSC1 pin and the RA6 pin is available for general purpose I/O.
The Oscillator Start-up Timer (OST) is disabled when EC mode is selected. Therefore, there is no delay in operation after a Power-on Reset (POR) or wake-up from Sleep. Because the PIC16c63a design is fully static, stopping the external clock input will have the effect of halting the device while leaving all data intact from microcontroller read out.
Upon restarting the external clock, the device will resume operation as if no time had elapsed in order to Read Out Secured PIC16C63A Microcontroller. The LP, XT and HS modes support the use of quartz crystal resonators or ceramic resonators connected to the OSC1 and OSC2 pins.
The mode selects a low, medium or high gain setting of the internal inverter-amplifier to support various resonator types and speed. LP Oscillator mode selects the lowest gain setting of the internal inverter-amplifier. LP mode current consumption is the least of the three modes from microcontroller reading out.
This mode is best suited to drive resonators with a low drive level specification, for example, tuning fork type crystals. XT Oscillator mode selects the intermediate gain setting of the internal inverter-amplifier. XT mode current consumption is the medium of the three modes.
This mode is best suited to drive resonators with a medium drive level specification, for example, low-frequency/AT-cut quartz crystal resonators. HS Oscillator mode selects the highest gain setting of the internal inverter-amplifier. HS mode current consumption is the highest of the three modes.
This mode is best suited for resonators that require a high drive setting, for example, high-frequency/AT-cut quartz crystal resonators or ceramic resonators.
