PIC18F8490 datasheet(49/414 Pages) MICROCHIP

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DS39629C-page 47

PIC18F6390/6490/8390/8490

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

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 3-8).

3.4.3

RC_IDLE MODE

In RC_IDLE mode, the CPU is disabled but the periph-

erals continue to be clocked from the internal oscillator

block using the INTOSC multiplexer. This mode allows

for controllable power conservation during Idle periods.

From RC_RUN, this mode is entered by setting the

IDLEN bit and executing a SLEEP instruction. If the

device is in another Run mode, first set IDLEN, then set

the SCS1 bit and execute SLEEP. Although its value is

ignored, it is recommended that SCS0 also be cleared;

this is to maintain software compatibility with future

devices. The INTOSC multiplexer may be used to

select a higher clock frequency by modifying the IRCF

bits before executing the SLEEP instruction. When the

clock source is switched to the INTOSC multiplexer, the

primary oscillator is shut down and the OSTS bit is

cleared.

If the IRCF bits are set to any non-zero value, or the

INTSRC bit is set, the INTOSC output is enabled. The

IOFS bit becomes set after the INTOSC output

becomes

stable

after

interval

TIOBST

(parameter 39, Table 26-10). Clocks to the peripherals

continue while the INTOSC source stabilizes. If the

IRCF bits were previously at a non-zero value, or

INTSRC was set before the SLEEP instruction was

executed and the INTOSC source was already stable,

the IOFS bit will remain set. If the IRCF bits and

INTSRC are all clear, the INTOSC output will not be

enabled; the IOFS bit will remain clear and there will be

no indication of the current clock source.

When a wake event occurs, the peripherals continue to

be clocked from the INTOSC multiplexer. After a delay

of TCSD following the wake event, the CPU begins

executing code being clocked by the INTOSC multi-

plexer. The IDLEN and SCS bits are not affected by the

wake-up. The INTRC source will continue to run if

either the WDT or the Fail-Safe Clock Monitor is

enabled.

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.

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