System Considerations
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
3-29
3.12.5
Recovery Times from Low Power Modes
The Modem Mode of operation is controlled by the MCU. The modem may be powered down if it is not
in use while the MCU is doing another task or while the whole node is “sleeping”, i.e., the MCU is also
powered down. Recovery time for both the modem and the MCU are important to system performance and
the recovery times are independent of each other.
3.12.5.1
Modem Low Power Mode Recovery Times
Each of the modem recovery times is from the low power condition to the Idle state. The start-up times for
the Off and Hibernate conditions are considerably longer due to the start-up of the voltage regulators and
clock oscillator.
shows a simplified state diagram for the low power modes and gives the
transition time to Idle:
•
Off > Idle (25 ms) - The Off state is released by negating M_RST high. From that time until the
modem asserts a ATTN interrupt and CLKO starts with a default frequency of 32.786+ kHz is 25
ms maximum
•
Hibernate > Idle (20 ms) - The Hibernate state is normally released via asserting ATTN low. The
startup time at 20 ms maximum is a little quicker than from the Off condition. The modem also
asserts a ATTN interrupt (if enabled) and CLKO starts (if enabled) with the value programmed
before entering Hibernate
•
Doze > Idle ((300 + 1/CLKO)
μ
s) - The Doze state can be released via a timer or asserting ATTN
low. The start-up time is considerably less ((300 + 1/CLKO)
μ
s) because the clock oscillator is
already running. CLKO can be programmed to run during Doze, and if not, CLKO will start in
enabled for normal operation. An ATTN interrupt will be asserted (if enabled) when ATTN is used
to exit Doze, or an interrupt will be asserted for exiting Doze Mode via a timer
Stop3 675 nA
Very low power. RAM and
registers contents maintained. I/O
states maintained.
Power not quite as low as
Stop2
Best choice for node “sleep”
function. Can maintain M_RST low
state.
300 nA
(adder for RTI)
RTI is used for wake up with
internal osc as clock source
RTI period has low
accuracy.
Can exit with RTI (uses internal
clock). Adds 300 nA to 675 nA IDD.
5
μ
A (adder for
osc enabled)
RTI is used for wake up with
external osc as clock source.
Allows use of crystal for clock
source for high accuracy
Additional current needed
for osc.
Can exit with RTI using crystal
source. Adds 5
μ
A to 675 nA Stop3
IDD
Wait
560
μ
A
(@ f
Bus
= 1 MHz)
Bus clock source remains active.
Clocks can be disabled to CPU
but peripherals can be clocked.
No recovery time. Reduced
power versus Run Mode.
Reduced noise for ADC readings.
Much higher power than
Stop modes. Voltage
regulator remains active.
Can be used with Run state for
lowest power when using
peripherals. Interrupts serviced
immediately. Not best choice for
node sleep mode.
Table 3-9. MC1321x MCU Low Power States (continued)
Mode
Current
(typ @ 3.0V)
Advantages
Disadvantages
Comment
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