PIC18F44J50-I Datasheet, PDF (52/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
4.4 Idle Modes
The Idle modes allow the controller’s CPU to be
selectively shut down while the peripherals continue to
operate. Selecting a particular Idle mode allows users
to further manage power consumption.
If the IDLEN bit is set to ‘1’ when a SLEEP instruction is
executed, the peripherals will be clocked from the clock
source selected using the SCS<1:0> bits; however, the
CPU will not be clocked. The clock source status bits are
not affected. Setting IDLEN and executing a SLEEP
instruction provides a quick method of switching from a
given Run mode to its corresponding Idle mode.
If the WDT is selected, the INTRC source will continue
to operate. If the Timer1 oscillator is enabled, it will also
continue to run.
Since the CPU is not executing instructions, the only
exits from any of the Idle modes are by interrupt, WDT
time-out or a Reset. When the CPU begins executing
code, it resumes with the same clock source for the
current Idle mode. For example, when waking from
RC_IDLE mode, the internal oscillator block will clock
the CPU and peripherals (in other words, RC_RUN
mode). The IDLEN and SCS bits are not affected by the
wake-up.
While in any Idle or Sleep mode, a WDT time-out will
result in a WDT wake-up to the Run mode currently
specified by the SCS<1:0> bits.
4.4.1 PRI_IDLE MODE
This mode is unique among the three low-power Idle
modes, in that it does not disable the primary device
clock. For timing-sensitive applications, this allows for
the fastest resumption of device operation with its more
accurate primary clock source, since the clock source
does not have to “warm up” or transition from another
oscillator.
PRI_IDLE mode is entered from PRI_RUN mode by
setting the IDLEN bit and executing a SLEEP instruc-
tion. If the device is in another Run mode, set IDLEN
first, then set the SCS bits to ‘00’ and execute SLEEP.
Although the CPU is disabled, the peripherals continue
to be clocked from the primary clock source specified
by the FOSC<1:0> Configuration bits. The OSTS bit
remains set (see Figure 4-7).
When a wake event occurs, the CPU is clocked from the
primary clock source. After the wake-up, the OSTS bit
remains set. The IDLEN and SCS bits are not affected
by the wake-up (see Figure 4-8).
4.4.2 SEC_IDLE MODE
In SEC_IDLE mode, the CPU is disabled but the
peripherals continue to be clocked from the Timer1
oscillator. This mode is entered from SEC_RUN by set-
ting the IDLEN bit and executing a SLEEP instruction. If
the device is in another Run mode, set IDLEN first, then
set SCS<1:0> to ‘01’ and execute SLEEP. When the
clock source is switched to the Timer1 oscillator, the
primary oscillator is shut down (unless some other
peripheral is still requesting it), the OSTS bit is cleared
and the T1RUN bit is set.
When a wake event occurs, the peripherals continue to
be clocked from the Timer1 oscillator. After a wake
event, the CPU begins executing code being clocked
by the Timer1 oscillator. The IDLEN and SCS bits are
not affected by the wake-up; the Timer1 oscillator
continues to run (see Figure 4-8).
Note:
The Timer1 oscillator should already be
running prior to entering SEC_IDLE
mode. If the T1OSCEN bit is not set when
the SLEEP instruction is executed, the
SLEEP instruction will be ignored and
entry to SEC_IDLE mode will not occur. If
the Timer1 oscillator is enabled, but not
yet running, peripheral clocks will be
delayed until the oscillator has started. In
such situations, initial oscillator operation
is far from stable and unpredictable
operation may result.
FIGURE 4-7:
OSC1
CPU Clock
Peripheral
Clock
Program
Counter
TRANSITION TIMING FOR ENTRY TO IDLE MODE
Q1
Q2
Q3
Q4
Q1
PC
PC + 2
DS39931D-page 52
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