PIC18F2220/2320/4220/4320
When a wake-up event occurs, the peripherals continue
to be clocked from the Timer1 oscillator. After a 10 µs
delay following the wake-up event, the CPU begins exe-
cuting code, being clocked by the Timer1 oscillator. The
microcontroller operates in SEC_RUN mode until the
primary clock becomes ready. When the primary clock
becomes ready, a clock switch back to the primary clock
occurs (see Figure 3-6). When the clock switch is com-
plete, the T1RUN bit is cleared, the OSTS bit is set and
the primary clock is providing the system clock. The
IDLEN and SCS bits are not affected by the wake-up;
the Timer1 oscillator continues to run.
3.3.2
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 by setting the IDLEN
bit, modifying to SCS1:SCS0 = 01 and executing a
SLEEPinstruction. When the clock source is switched
to the Timer1 oscillator (see Figure 3-5), the primary
oscillator is shut down, the OSTS bit is cleared and the
T1RUN bit is set.
Note:
The Timer1 oscillator should already be
running prior to entering SEC_IDLE mode.
If the T1OSCEN bit is not set when try-
ing to set the SCS0 bit (OSCCON<0>),
the write to SCS0 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 sit-
uations, initial oscillator operation is far
from stable and unpredictable operation
may result.
FIGURE 3-5:
TIMING TRANSITION FOR ENTRY TO SEC_IDLE MODE
Q1 Q2 Q3 Q4 Q1
1
2
3
4
5
6
7
8
T1OSI
OSC1
Clock Transition
CPU
Clock
Peripheral
Clock
Program
Counter
PC
PC + 2
FIGURE 3-6:
TIMING TRANSITION FOR WAKE FROM SEC_RUN MODE (HSPLL)
Q3
Q4
Q1
Q2 Q3 Q4 Q1 Q2 Q3
Q1
Q2
T1OSI
OSC1
(1)
(1)
TOST
TPLL
PLL Clock
Output
1
2
3
4
5
6
7
8
Clock Transition
CPU Clock
Peripheral
Clock
Program
Counter
PC + 4
PC + 6
PC
PC + 2
OSTS bit Set
Note 1: TOST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
Wake-up from Interrupt Event
DS39599C-page 34
2003 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
