C8051F340-GQR Datasheet, PDF (133/276 Pages) Silicon Laboratories – Full Speed USB Flash MCU Family

C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D
SFR Definition 14.2. OSCICL: Internal H-F Oscillator Calibration
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Reset Value
-
-
-
OSCCAL
Variable
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0 SFR Address:
0xB3
Bits4–0:
OSCCAL: Oscillator Calibration Value
These bits determine the internal H-F oscillator period. When set to 00000b, the oscillator
operates at its fastest setting. When set to 11111b, the oscillator operates at is slowest set-
ting. The contents of this register are factory calibrated to produce a 12 MHz internal oscilla-
tor frequency.
Note: The contents of this register are undefined when Clock Recovery is enabled. See Section
“16.4. USB Clock Configuration” on page 166 for details on Clock Recovery.
14.2. Programmable Internal Low-Frequency (L-F) Oscillator
The C8051F340/1/2/3/4/5/8/9/C/D devices include a programmable internal oscillator which operates at a
nominal frequency of 80 kHz. The low-frequency oscillator circuit includes a divider that can be changed to
divide the clock by 1, 2, 4, or 8, using the OSCLD bits in the OSCLCN register (see SFR Definition 14.3).
Additionally, the OSCLF bits (OSCLCN5:2) can be used to adjust the oscillator’s output frequency.
14.2.1. Calibrating the Internal L-F Oscillator
Timers 2 and 3 include capture functions that can be used to capture the oscillator frequency, when run-
ning from a known time base. When either Timer 2 or Timer 3 is configured for L-F Oscillator Capture
Mode, a falling edge (Timer 2) or rising edge (Timer 3) of the low-frequency oscillator’s output will cause a
capture event on the corresponding timer. As a capture event occurs, the current timer value
(TMRnH:TMRnL) is copied into the timer reload registers (TMRnRLH:TMRnRLL). By recording the differ-
ence between two successive timer capture values, the low-frequency oscillator’s period can be calcu-
lated. The OSCLF bits can then be adjusted to produce the desired oscillator period.
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