Power Management
MCF52277 Reference Manual, Rev. 1
Freescale Semiconductor
8-7
8.2.5
Low-Power Control Register (LPCR)
The LPCR register controls chip operation and module operation during low-power modes.
8.3
Functional Description
This section discusses the functions and characteristics of the low-power modes, and how each module is
affected by, or affects these modes.
8.3.1
Peripheral Shut Down
All peripherals, except for the SCM and crossbar switch, may have the software remove their input clocks
individually to reduce power consumption. See
Section 8.2.4, “Peripheral Power Management Registers
for more information. A peripheral may be disabled at any time and remains
disabled during any low-power mode of operation.
Address: 0xFC0A_0007 (LPCR)
Access: Supervisor read/write
7
6
5
4
3
2
1
0
R
0
0
FWKUP
STPMD
0
0
0
W
Reset:
0
0
0
0
0
0
0
0
Figure 8-6. Low-Power Control Register (LPCR)
Table 8-8. LPCR Field Descriptions
Field
Description
7–6
Reserved, must be cleared.
5
FWKUP
Fast wake-up. Determines whether the system clocks are enabled upon wake-up from stop mode. This bit must be
written before execution of the STOP instruction for it to take effect.
0 System clocks enabled only when PLL is locked or operating normally.
1 System clocks enabled upon wake-up from stop mode, regardless of PLL lock status.
Note:
Setting this bit is potentially dangerous and unreliable. The system may behave unpredictably when using an
unlocked clock because the clock frequency could overshoot the maximum frequency of the device.
Note:
If FWKUP is set before entering stop mode, it should not be cleared upon wake-up from stop mode until after
the PLL has actually acquired lock. Lock status may be obtained by reading PLL status register. Because the
PLL never locks in limp mode, the FWKUP is ineffective. The system clocks are always enabled upon wake-up
from stop mode, regardless of the value of FWKUP.
4–3
STPMD
FB_CLK stop mode bits. Controls the operation of the clocks, PLL, and oscillator in stop mode:
2–0
Reserved, must be cleared.
STPMD
System Clocks
FB_CLK
PLL
Oscillator
00
Disabled
Enabled
Enabled
Enabled
01
Disabled
Disabled
Enabled
Enabled
10
Disabled
Disabled
Disabled
Enabled
11
Disabled
Disabled
Disabled
Disabled
Содержание MCF52277
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