PIC18F97J60 FAMILY
3.0
POWER-MANAGED MODES
3.1.1
CLOCK SOURCES
The PIC18F97J60 family devices provide the ability to
manage power consumption by simply managing clock-
ing to the CPU and the peripherals. In general, a lower
clock frequency and a reduction in the number of circuits
being clocked constitutes lower consumed power. For
the sake of managing power in an application, there are
three primary modes of operation:
• Run mode
• Idle mode
• Sleep mode
These modes define which portions of the device are
clocked and at what speed. The Run and Idle modes
may use any of the three available clock sources
(primary, secondary or internal oscillator block); the
Sleep mode does not use a clock source.
The power-managed modes include several
power-saving features offered on previous PIC
®
MCU
devices. One is the clock switching feature, offered in
other PIC18 devices, allowing the controller to use the
Timer1 oscillator in place of the primary oscillator. Also
included is the Sleep mode, offered by all PIC MCU
devices, where all device clocks are stopped.
The SCS1:SCS0 bits allow the selection of one of three
clock sources for power-managed modes. They are:
• The primary clock, as defined by the
FOSC2:FOSC0 Configuration bits
• The secondary clock (Timer1 oscillator)
• The internal oscillator
3.1.2
ENTERING POWER-MANAGED
MODES
Switching from one power-managed mode to another
begins by loading the OSCCON register. The
SCS1:SCS0 bits select the clock source and determine
which Run or Idle mode is to be used. Changing these
bits causes an immediate switch to the new clock
source, assuming that it is running. The switch may
also be subject to clock transition delays. These are
discussed in
and subsequent sections.
Entry to the power-managed Idle or Sleep modes is
triggered by the execution of a
SLEEP
instruction. The
actual mode that results depends on the status of the
IDLEN bit.
Depending on the current mode and the mode being
switched to, a change to a power-managed mode does
not always require setting all of these bits. Many
transitions may be done by changing the oscillator
select bits, or changing the IDLEN bit, prior to issuing a
SLEEP
instruction. If the IDLEN bit is already
configured correctly, it may only be necessary to
perform a
SLEEP
instruction to switch to the desired
mode.
3.1
Selecting Power-Managed Modes
Selecting a power-managed mode requires two
decisions: if the CPU is to be clocked or not and which
clock source is to be used. The IDLEN bit
(OSCCON<7>) controls CPU clocking, while the
SCS1:SCS0 bits (OSCCON<1:0>) select the clock
source. The individual modes, bit settings, clock sources
and affected modules are summarized in Table 3-1.
TABLE 3-1:
Mode
Sleep
PRI_RUN
SEC_RUN
RC_RUN
PRI_IDLE
SEC_IDLE
RC_IDLE
Note 1:
POWER-MANAGED MODES
OSCCON<7,1:0>
IDLEN
(1)
0
N/A
N/A
N/A
1
1
1
SCS1:SCS0
N/A
10
01
11
10
01
11
Module Clocking
CPU
Off
Clocked
Clocked
Clocked
Off
Off
Off
Peripherals
Off
Clocked
Clocked
Clocked
Clocked
Clocked
Clocked
Available Clock and Oscillator Source
None – All clocks are disabled
Primary – HS, EC, HSPLL, ECPLL;
this is the normal, full-power execution mode
Secondary – Timer1 Oscillator
Internal Oscillator
Primary – HS, EC, HSPLL, ECPLL
Secondary – Timer1 Oscillator
Internal Oscillator
IDLEN reflects its value when the
SLEEP
instruction is executed.
©
2009 Microchip Technology Inc.
DS39762E-page 49
MICROCHIP [ MICROCHIP TECHNOLOGY ]
