C8051F50x-F51x
19.2. Programmable Internal Oscillator
All C8051F50x-F51x devices include a programmable internal high-frequency oscillator that defaults as
the system clock after a system reset. The internal oscillator period can be adjusted via the OSCICRS and
OSCIFIN registers defined in SFR Definition 19.3 and SFR Definition 19.4. On C8051F50x-F51x devices,
OSCICRS and OSCIFIN are factory calibrated to obtain a 24 MHz base frequency. Note that the system
clock may be derived from the programmed internal oscillator divided by 1, 2, 4, 8, 16, 32, 64, or 128, as
defined by the IFCN bits in register OSCICN. The divide value defaults to 128 following a reset.
19.2.1. Internal Oscillator Suspend Mode
When software writes a logic 1 to SUSPEND (OSCICN.5), the internal oscillator is suspended. If the sys-
tem clock is derived from the internal oscillator, the input clock to the peripheral or CIP-51 will be stopped
until one of the following events occur:
Port 0 Match Event.
Port 1 Match Event.
Comparator 0 enabled and output is logic 0.
When one of the oscillator awakening events occur, the internal oscillator, CIP-51, and affected peripherals
resume normal operation, regardless of whether the event also causes an interrupt. The CPU resumes
execution at the instruction following the write to SUSPEND.
Rev. 1.1
167
SILABS [ SILICON LABORATORIES ]
