Datasheet

 2010 Microchip Technology Inc. Preliminary DS39964B-page 49
PIC18F47J53 FAMILY
4.2 Run Modes
In the Run modes, clocks to both the core and
peripherals are active. The difference between these
modes is the clock source.
4.2.1 PRI_RUN MODE
The PRI_RUN mode is the normal, full-power execu-
tion mode of the microcontroller. This is also the default
mode upon a device Reset unless Two-Speed Start-up
is enabled (see Section 28.4 “Two-Speed Start-up”
for details). In this mode, the OSTS bit is set (see
Section 3.5.1 “Oscillator Control Register”).
4.2.2 SEC_RUN MODE
The SEC_RUN mode is the compatible mode to the
“clock switching” feature offered in other PIC18
devices. In this mode, the CPU and peripherals are
clocked from the Timer1 oscillator. This gives users the
option of low-power consumption while still using a
high-accuracy clock source.
SEC_RUN mode is entered by setting the SCS<1:0>
bits to ‘01’. The device clock source is switched to the
Timer1 oscillator (see Figure 4-1), the primary
oscillator is shut down, the SOSCRUN bit
(OSCCON2<6>) is set and the OSTS bit is cleared.
On transitions from SEC_RUN mode to PRI_RUN
mode, the peripherals and CPU continue to be clocked
from the Timer1 oscillator while the primary clock is
started. When the primary clock becomes ready, a
clock switch back to the primary clock occurs (see
Figure 4-2). When the clock switch is complete, the
SOSCRUN bit is cleared, the OSTS bit is set and the
primary clock would be providing the clock. The IDLEN
and SCS bits are not affected by the wake-up; the
Timer1 oscillator continues to run.
FIGURE 4-1: TRANSITION TIMING FOR ENTRY TO SEC_RUN MODE
FIGURE 4-2: TRANSITION TIMING FROM SEC_RUN MODE TO PRI_RUN MODE (HSPLL)
Note: The Timer1 oscillator should already be
running prior to entering SEC_RUN mode.
If the T1OSCEN bit is not set when the
SCS<1:0> bits are set to ‘01’, entry to
SEC_RUN mode will not occur. If the
Timer1 oscillator is enabled, but not yet
running, device clocks will be delayed until
the oscillator has started. In such situa-
tions, initial oscillator operation is far from
stable and unpredictable operation may
result.
Q4Q3Q2
OSC1
Peripheral
Program
Q1
T1OSI
Q1
Counter
Clock
CPU
Clock
PC + 2PC
123 n-1n
Clock Transition
Q4Q3Q2 Q1 Q3Q2
PC + 4
Q1 Q3 Q4
OSC1
Peripheral
Program
PC
T1OSI
PLL Clock
Q1
PC + 4
Q2
Output
Q3 Q4 Q1
CPU Clock
PC + 2
Clock
Counter
Q2 Q2 Q3
Note 1: TOST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
SCS<1:0> Bits Changed
TPLL
(1)
12 n-1n
Clock
OSTS Bit Set
Transition
TOST
(1)