Microchip Technology ARD00385 Data Sheet
2009-2011 Microchip Technology Inc.
DS39957D-page 55
PIC18F87K90 FAMILY
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 LF-INTOSC 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 LF-INTOSC or INTOSC (MF-INTOSC or
HF-INTOSC) – there are no distinguishable differences
between the PRI_RUN and RC_RUN modes during
execution. Entering or exiting RC_RUN mode,
however, causes a clock switch delay. Therefore, if the
primary clock source is the internal oscillator block,
using RC_RUN mode is not recommended.
clocked from the internal oscillator block using the
INTOSC multiplexer. In this mode, the primary clock is
shut down. When using the LF-INTOSC 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 LF-INTOSC or INTOSC (MF-INTOSC or
HF-INTOSC) – there are no distinguishable differences
between the PRI_RUN and RC_RUN modes during
execution. Entering or exiting RC_RUN mode,
however, causes a clock switch delay. Therefore, if the
primary clock source is the internal oscillator block,
using RC_RUN mode is not recommended.
This mode is entered by setting the SCS1 bit to ‘1’. To
maintain software compatibility with future devices, it is
recommended that the SCS0 bit also be cleared, even
though the bit is ignored. When the clock source is
switched to the INTOSC multiplexer (see
maintain software compatibility with future devices, it is
recommended that the SCS0 bit also be cleared, even
though the bit is ignored. When the clock source is
switched to the INTOSC multiplexer (see
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.
cleared. The IRCF bits may be modified at any time to
immediately change the clock speed.
Q4
Q3
Q2
OSC1
Peripheral
Program
Q1
SOSCI
Q1
Counter
Clock
CPU
Clock
PC + 2
PC
1
2
3
n-1
n
Clock Transition
(1)
Q4
Q3
Q2
Q1
Q3
Q2
PC + 4
Note 1:
Clock transition typically occurs within 2-4 T
OSC
.
Q1
Q3 Q4
OSC1
Peripheral
Program
PC
SOSC
PLL Clock
Q1
PC + 4
Q2
Output
Q3
Q4
Q1
CPU Clock
PC + 2
Clock
Counter
Q2
Q2
Q3
Note 1:
T
OST
= 1024 T
OSC
; T
PLL
= 2 ms (approx). These intervals are not shown to scale.
2:
Clock transition typically occurs within 2-4 T
OSC
.
SCS<1:0> bits Changed
T
PLL(1)
1
2
n-1 n
Clock
OSTS bit Set
Transition
(2)
T
OST(1)
Note:
Caution should be used when modifying a
single IRCF bit. At a lower V
single IRCF bit. At a lower V
DD
, it is
possible to select a higher clock speed
than is supportable by that V
than is supportable by that V
DD
. Improper
device operation may result if the V
DD
/
F
OSC
specifications are violated.