C8051F330_07 Datasheet, PDF (117/216 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F330/1/2/3/4/5
13.2. Programmable Internal Low-Frequency (L-F) Oscillator
All C8051F330/1/2/3/4/5 devices include a programmable low-frequency internal oscillator, which is cali-
brated to 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 Defi-
nition 13.3). Additionally, the OSCLF bits (OSCLCN5:2) can be used to adjust the oscillator’s output fre-
quency.
13.2.1. 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 frequency.
SFR Definition 13.3. OSCLCN: Internal L-F Oscillator Control
R/W
R
R/W
OSCLEN OSCLRDY OSCLF3
Bit7
Bit6
Bit5
R/W
OSCLF2
Bit4
R/W
OSCLF1
Bit3
R/W
OSCLF0
Bit2
R/W
OSCLD1
Bit1
R/W
Reset Value
OSCLD0 00vvvv00
Bit0 SFR Address:
0xE3
Bit7:
Bit6:
Bits5–2:
Bits1–0:
OSCLEN: Internal L-F Oscillator Enable.
0: Internal L-F Oscillator Disabled.
1: Internal L-F Oscillator Enabled.
OSCLRDY: Internal L-F Oscillator Ready.
0: Internal L-F Oscillator frequency not stabilized.
1: Internal L-F Oscillator frequency stabilized.
OSCLF[3:0]: Internal L-F Oscillator Frequency Control bits.
Fine-tune control bits for the Internal L-F oscillator frequency. When set to 0000b, the L-F
oscillator operates at its fastest setting. When set to 1111b, the L-F oscillator operates at its
slowest setting.
OSCLD[1:0]: Internal L-F Oscillator Divider Select.
00: Divide by 8 selected.
01: Divide by 4 selected.
10: Divide by 2 selected.
11: Divide by 1 selected.
Rev. 1.5
117