PIC18F87J10 Datasheet, PDF (40/394 Pages) Microchip Technology – 64/80-Pin High-Performance, 1-Mbit Flash Microcontrollers with nanoWatt Technology

PIC18F87J10 FAMILY
3.2.3 RC_RUN MODE
In RC_RUN mode, the CPU and peripherals are
clocked from the internal oscillator; the primary clock is
shut-down. This mode provides the best power conser-
vation of all the Run modes, while still executing code.
It works well for user applications which are not highly
timing sensitive or do not require high-speed clocks at
all times.
This mode is entered by setting SCS to ‘11’. When the
clock source is switched to the INTRC (see Figure 3-3),
the primary oscillator is shut-down and the OSTS bit is
cleared.
On transitions from RC_RUN mode to PRI_RUN mode,
the device continues to be clocked from the INTRC
while the primary clock is started. When the primary
clock becomes ready, a clock switch to the primary
clock occurs (see Figure 3-4). When the clock switch is
complete, the OSTS bit is set and the primary clock is
providing the device clock. The IDLEN and SCS bits
are not affected by the switch. The INTRC source will
continue to run if either the WDT or the Fail-Safe Clock
Monitor is enabled.
FIGURE 3-3:
TRANSITION TIMING TO RC_RUN MODE
Q1 Q2 Q3 Q4 Q1
INTRC
1
OSC1
CPU
Clock
Peripheral
Clock
Program
Counter
PC
2
3
n-1 n
Clock Transition
PC + 2
Q2 Q3 Q4 Q1 Q2 Q3
PC + 4
FIGURE 3-4:
TRANSITION TIMING FROM RC_RUN MODE TO PRI_RUN MODE
INTRC
Q1
Q2
Q3
Q4 Q1
Q2 Q3 Q4 Q1 Q2 Q3
OSC1
PLL Clock
Output
TOST⁽¹⁾
CPU Clock
Peripheral
Clock
Program
Counter
PC
SCS1:SCS0 bits Changed
TPLL⁽¹⁾
1 2 n-1 n
Clock
Transition
OSTS bit Set
PC + 2
Note 1: TOST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
PC + 4
DS39663A-page 38
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