
2007 Microchip Technology Inc.
Preliminary
DS39625C-page 35
PIC18F2585/2680/4585/4680
FIGURE 3-1:
TRANSITION TIMING FOR ENTRY TO SEC_RUN MODE
FIGURE 3-2:
TRANSITION TIMING FROM SEC_RUN MODE TO PRI_RUN MODE (HSPLL)
3.2.3
RC_RUN MODE
In RC_RUN mode, the CPU and peripherals are
clocked from the internal oscillator block using the
INTOSC multiplexer; 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 distin-
guishable
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 SCS1 to ‘1’. Although
it is ignored, it is recommended that SCS0 also be
cleared; this is to maintain software compatibility with
future devices. When the clock source is switched to
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
12
3
n-1
n
Clock Transition
Q4
Q3
Q2
Q1
Q3
Q2
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
Q3
Note 1: TOST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
SCS1:SCS0 bits changed
TOST(1)
TPLL(1)
12
n-1
n
Clock
OSTS bit set
Transition
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.