MC68LC302 Datasheet, PDF (26/169 Pages) Motorola, Inc – Low Power Integrated Multiprotocol Processor Reference Manual

Configuration, Clocking, Low Power Modes, and Internal Memory Map
2.4.4 IMP Power Management
The IMP portion of the MC68LC302 has several low power modes from which to choose.
2.4.4.1 IMP LOW POWER MODES. The MC68LC302 provides a number of low power
modes for the IMP section. Each of the operation modes has different current consumption,
wake-up time, and functionality characteristics. The state of the IMP’s 68000 data and
address bus lines can be either driven high, low or high impedance during low power stop
mode by programming the low power drive control register (LPDCR).
NOTE
For lowest current consumption, the SCCs and BRGs should be
disabled before entering the low power modes. Current con-
sumption for all operating modes is specified in Section 6 Elec-
trical Characteristics.
Operation
Mode
STOP
DOZE
STAND_BY
SLOW_GO/
NORMAL
Table 2-3. IMP Low Power Modes - IMP PLL Enabled
Oscillator
Not Active
Active
Active
Active
PLL
Wake_Up
IMP Clock (Osc. Clock
Cycles)
Current
Consumption ^{Method of Entry/}
IMP
LPM bits
Functionality
(Approximate)
Not active Not active
70000 osc.
clocks
<0.1mA
Stop instruction/
LPM1–0=11
No
Not active Not active
2500 osc
clocks
About 500uA
Stop instruction/
LPM1–0=10
No
Active (if
enabled
Not active
2–5 system
clock cycles
About 5mA
Stop instruction/ Partial (BRG
LPM1–0=01 clock is active)
Active (if
enabled)
Active
Low, depends on
CLK freq.
Write to DF3–0
Full
2.4.4.1.1 STOP Mode. In STOP mode, all parts of IMP are inactive and the current con-
sumption is less than 0.1mA. Both the crystal oscillator and the IMP PLL are shut down.
Because both the oscillator and the PLL must start up, the wake-up time takes 70000
EXTAL clocks (for example, 70000 cycles of 32.768 kHz crystal will take about 2.2 seconds).
The STOP mode is entered by executing the STOP instruction with the LPM0–1 bits in the
IOMCR register set to 11. Refer to 2.4.4.2.2 Entering the STOP/ DOZE/ STAND_BY Mode
for an example instruction sequence for use with the STOP instruction.
2.4.4.1.2 DOZE Mode. In DOZE mode, the oscillator is active in the IMP but the IMP PLL is
shut down. The current consumption depends on the frequency of the external crystal but is
on the order of 500 µA. In DOZE mode, the IMP is shut down. The wake-up time is 2500
cycles of the external crystal (for example, 2500 cycles of 32.768 kHz crystal will take about
80 milliseconds.). Doze mode has faster wake-up time than the STOP mode, at the price of
higher current consumption.
The DOZE mode is entered by executing the STOP instruction with the LPM1–0 bits in the
IOMCR register set to 10. Refer to 2.4.4.2.2 Entering the STOP/ DOZE/ STAND_BY Mode
for an example instruction sequence for use with the STOP instruction.
2.4.4.1.3 STAND_BY Mode. In STAND_BY mode, the oscillator is active, and the IMP PLL,
if enabled, is active but the IMP clock is not active and the IMP is shut down. Current con-
MOTOROLA
MC68LC302 REFERENCE MANUAL
2-13