PIC18F2455_09 Datasheet, PDF (43/438 Pages) Microchip Technology – 28/40/44-Pin,High-Performance,Enhanced Flash,USB Microcontrollers with nanoWatt Technology

PIC18F2455/2550/4455/4550
3.4.1 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 clear the SCS bits and execute SLEEP.
Although the CPU is disabled, the peripherals continue
to be clocked from the primary clock source specified
by the FOSC3:FOSC0 Configuration bits. The OSTS
bit remains set (see Figure 3-7).
When a wake event occurs, the CPU is clocked from the
primary clock source. A delay of interval TCSD is
required between the wake event and when code
execution starts. This is required to allow the CPU to
become ready to execute instructions. After the
wake-up, the OSTS bit remains set. The IDLEN and
SCS bits are not affected by the wake-up (see
Figure 3-8).
3.4.2 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 SCS1:SCS0 to ‘01’ and execute SLEEP. When the
clock source is switched to the Timer1 oscillator, the
primary oscillator is shut down, 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 an interval
of TCSD following the wake event, the CPU begins exe-
cuting 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 3-8).
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 3-7:
OSC1
CPU Clock
Peripheral
Clock
Program
Counter
TRANSITION TIMING FOR ENTRY TO IDLE MODE
Q1
Q2
Q3
Q4
Q1
PC
PC + 2
FIGURE 3-8:
TRANSITION TIMING FOR WAKE FROM IDLE TO RUN MODE
Q1
OSC1
CPU Clock
Peripheral
Clock
Program
Counter
TCSD
Wake Event
Q2
Q3
Q4
PC
© 2009 Microchip Technology Inc.
DS39632E-page 41