c8051t602 Silicon Laboratories, c8051t602 Datasheet - Page 93

• Manufacturer Part Number: c8051t602
• Description: Mixed Signal Otp Eprom Mcu Family
• Manufacturer: Silicon Laboratories

C8051T600/1/2/3/4/5
12.2. External Oscillator Circuit
The external oscillator circuit can accept an external CMOS clock, or operate from an external capacitor or
RC circuit applied to the EXTCLK pin (P0.3). To operate in external CMOS mode, the EXTCLK pin should
be configured as a digital input. For capacitor or RC mode, the EXTCLK pin should be configured as an
analog input. See
Section “13.2. Port I/O Initialization” on page 99
for details on Port input mode selec-
tion. Whenever an external clock option is used, the Port I/O Crossbar should be configured to skip the
EXTCLK pin. See
Section “13.1. Priority Crossbar Decoder” on page 98
for Crossbar configuration
details. Note that the external oscillator control settings should not be changed while running the processor
from an external oscillator source.
12.3. System Clock Selection
The CLKSL bit in register OSCICN selects which oscillator is used as the system clock. CLKSL must be
set to ‘1’ for the system clock to run from an external clock source; however, the external clock may still
clock peripherals (timers, PCA) when the internal oscillator is selected as the system clock. The system
clock may be switched on-the-fly between the internal and external clock sources, so long as the selected
oscillator is enabled and has settled. The internal oscillator requires very little start-up time and may be
enabled and selected as the system clock in the same write to OSCICN. When switching between internal
and external clock sources, the hand-off to the other clock source lasts two clock cycles of the slower
clock.
Rev. 0.5
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