PIC18F44J10 datasheet(38/368 Pages) MICROCHIP

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PIC18F45J10 FAMILY

DS39682E-page 36

4.1.3

CLOCK TRANSITIONS AND STATUS

INDICATORS

The length of the transition between clock sources is

the sum of two cycles of the old clock source and three

to four cycles of the new clock source. This formula

assumes that the new clock source is stable.

Two bits indicate the current clock source and its

status:

OSTS

(OSCCON<3>)

and

T1RUN

(T1CON<6>). In general, only one of these bits will be

set while in a given power-managed mode. When the

OSTS bit is set, the primary clock is providing the

device clock. When the T1RUN bit is set, the Timer1

oscillator is providing the clock. If neither of these bits

is set, INTRC is clocking the device.

4.1.4

MULTIPLE SLEEP COMMANDS

The power-managed mode that is invoked with the

SLEEP

instruction is determined by the setting of the

IDLEN bit at the time the instruction is executed. If

another SLEEP instruction is executed, the device will

enter the power-managed mode specified by IDLEN at

that time. If IDLEN has changed, the device will enter the

new power-managed mode specified by the new setting.

4.2

Run Modes

In the Run modes, clocks to both the core and

peripherals are active. The difference between these

modes is the clock source.

4.2.1

PRI_RUN MODE

The PRI_RUN mode is the normal, full-power execu-

tion mode of the microcontroller. This is also the default

mode upon a device Reset unless Two-Speed Start-up

is enabled (see Section 21.4 “Two-Speed Start-up”

for details). In this mode, the OSTS bit is set. (see

Section 3.6.1 “Oscillator Control Register”

4.2.2

SEC_RUN MODE

The SEC_RUN mode is the compatible mode to the

“clock switching” feature offered in other PIC18

devices. In this mode, the CPU and peripherals are

clocked from the Timer1 oscillator. This gives users the

option of lower power consumption while still using a

high-accuracy clock source.

SEC_RUN mode is entered by setting the SCS<1:0>

bits to ‘01’. The device clock source is switched to the

Timer1 oscillator (see Figure 4-1), the primary

oscillator is shut down, the T1RUN bit (T1CON<6>) is

set and the OSTS bit is cleared.

On transitions from SEC_RUN mode to PRI_RUN

mode, the peripherals and CPU continue to be clocked

from the Timer1 oscillator while the primary clock is

started. When the primary clock becomes ready, a

clock switch back to the primary clock occurs (see

Figure 4-2). When the clock switch is complete, the

T1RUN bit is cleared, the OSTS bit is set and the

primary clock is providing the clock. The IDLEN and

SCS bits are not affected by the wake-up; the Timer1

oscillator continues to run.

FIGURE 4-1:

TRANSITION TIMING FOR ENTRY TO SEC_RUN MODE

Note:

Executing a SLEEP instruction does not

necessarily place the device into Sleep

mode. It acts as the trigger to place the

controller into either Sleep mode or one of

the Idle modes, depending on the setting

of the IDLEN bit.

Note:

The Timer1 oscillator should already be

running prior to entering SEC_RUN mode.

If the T1OSCEN bit is not set when the

SCS<1:0> bits are set to ‘01’, entry to

SEC_RUN mode will not occur. If the

Timer1 oscillator is enabled, but not yet

running, device clocks will be delayed until

the oscillator has started. In such situa-

tions, initial oscillator operation is far from

stable and unpredictable operation may

result.

OSC1

Peripheral

Program

T1OSI

Counter

Clock

CPU

Clock

PC + 2

n-1

Clock Transition

PC + 4

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