
PIC18F1230/1330
2009 Microchip Technology Inc.
DS39758D-page 33
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)
4.2.3
RC_RUN MODE
In RC_RUN mode, the CPU and peripherals are
clocked from the internal oscillator block using the
INTOSC multiplexer. In this mode, the primary clock is
shut down. When using the INTRC source, this mode
provides the best power conservation 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.
If the primary clock source is the internal oscillator block
(either INTRC or INTOSC), there are no distinguishable
differences between PRI_RUN and RC_RUN modes
during execution. However, a clock switch delay will
occur during entry to and exit from RC_RUN mode.
Therefore, if the primary clock source is the internal
oscillator block, the use of RC_RUN mode is not
recommended.
This mode is entered by setting the SCS1 bit to ‘1’.
Although it is ignored, it is recommended that the SCS0
bit also be cleared; this is to maintain software compat-
ibility with future devices. When the clock source is
switched to the INTOSC multiplexer (see
Figure 4-3),
the primary oscillator is shut down and the OSTS bit is
cleared. The IRCF bits may be modified at any time to
immediately change the clock speed.
Q4
Q3
Q2
OSC1
Peripheral
Program
Q1
T1OSI
Q1
Counter
Clock
CPU
Clock
PC + 2
PC
123
n-1
n
Clock Transition(1)
Q4
Q3
Q2
Q1
Q3
Q2
PC + 4
Note 1:
Clock transition typically occurs within 2-4 TOSC.
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
Q3
Note 1:
TOST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
2:
Clock transition typically occurs within 2-4 TOSC.
SCS1:SCS0 bits Changed
TPLL(1)
12
n-1 n
Clock
OSTS bit Set
Transition(2)
TOST(1)
Note:
Caution should be used when modifying a
single IRCF bit. If VDD is less than 3V, it is
possible to select a higher clock speed
than is supported by the low VDD.
Improper device operation may result if
the VDD/FOSC specifications are violated.