PIC16LF1454 Datasheet, PDF (73/418 Pages) Microchip Technology – 14/20-Pin Flash, 8-Bit USB Microcontrollers with XLP Technology

PIC16(L)F1454/5/9
5.8 Active Clock Tuning (ACT)
The Active Clock Tuning (ACT) continuously adjusts
the 16 MHz Internal Oscillator, using an available
external reference, to achieve ± 0.20% accuracy. This
eliminates the need for a high-speed, high-accuracy
external crystal when the system has an available
lower speed, lower power, high-accuracy clock source
available.
Systems implementing a Real-Time Clock Calendar
(RTCC) or a full-speed USB application can take full
advantage of the ACT.
5.8.1
ACTIVE CLOCK TUNING
OPERATION
The ACT defaults to the disabled state after any Reset.
When the ACT is disabled, the user can write to the
TUN<6:0> bits in the OSCTUNE register to manually
adjust the 16 MHz Internal Oscillator.
The ACT is enabled by setting the ACTEN bit of the
ACTCON register. When enabled, the ACT takes
control of the OSCTUNE register. The ACT uses the
selected ACT reference clock to tune the 16 MHz
Internal Oscillator to an accuracy of 16MHz ± 0.2%.
The tuning automatically adjusts the OSCTUNE
register every reference clock cycle.
Note 1: When the ACT is enabled, the
OSCTUNE register is only updated by
the ACT. Writes to the OSCTUNE regis-
ter by the user are inhibited, but reading
the register is permitted.
2: After disabling the ACT, the user should
wait three instructions before writing to
the OSCTUNE register.
5.8.2
ACTIVE CLOCK TUNING SOURCE
SELECTION
The ACT reference clock is selected with the ACTSRC
bit of the ACTCON register. The reference clock
sources are provided by the:
• USB module in full-speed operation (ACT_clk)
• Secondary clock at 32.768 kHz (SOSC_clk)
5.8.3 ACT LOCK STATUS
The ACTLOCK bit will be set to '1', when the 16 MHz
Internal Oscillator is successfully tuned.
The bit will be cleared by the following conditions:
• Out of Lock condition
• Device Reset
• ACT is disabled
5.8.4 ACT OUT-OF-RANGE STATUS
If the ACT requires an OSCTUNE value outside the
range to achieve ± 0.20% accuracy, then
the ACT Out-of-Range (ACTOR) Status bit will be set
to '1'.
An out-of-range status can occur:
• When the 16 MHz internal oscillator is tuned to its
lowest frequency and the next ACT_clk event
requests a lower frequency.
• When the 16 MHz internal oscillator is tuned to its
highest frequency and the next ACT_clk event
requests a higher frequency.
When the ACT out-of-range event occurs, the 16 MHz
internal oscillator will continue to use the last written
OSCTUNE value. When the OSCTUNE value moves
back within the tunable range and ACTLOCK is
established, the ACTOR bit is cleared to '0'.
FIGURE 5-11:
ACTIVE CLOCK TUNING BLOCK DIAGRAM
ACTSRC
ACTEN
FSUSB_clk
SOSC_clk
1 _{ACT_clk}
0
Enable
Active
Clock
Tuning
ACTUD
ACTEN
16 MHz
Internal OSC
ACT data
7
sfr data
7
OSCTUNE<6:0>
Write
OSCTUNE
ACTEN
 2012 Microchip Technology Inc.
Preliminary
DS41639A-page 73