NXP Semiconductors freescale semiconductor MC13211, Reference Manual

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System Considerations
MC1321x Reference Manual, Rev. 1.6
3-28 Freescale Semiconductor
3.12.4 MCU Low Power States
Table 3-9 lists the MCU low power states and the modes are covered in detail in Chapter 10, “MCU Modes
of Operation” . Also, a suggested application note for in-depth coverage of the MCU low power modes is
MC9S08GB/GT Low-Power Modes, AN2493 . There are three low power modes available:
• Stop1 - This MCU Mode IS NOT USABLE in the MC1321x device. The Stop1 is the off condition
for the MCU and does not allow the MCU I/O to retain their programmed states. As a result, there
is no means available to force the modem to a known condition on its reset input
• Stop2 - This is a very low power state in which the I/O states are maintained, the RAM contents
are maintained, and the RTI can be used to exit with the internal oscillator. This state can maintain
a reset condition on the modem. The disadvantages are that the register values are reset so they
must be restored before peripherals can be used and interrupts are not serviced, but instead are
treated as a reset
• Stop3 - This is still a very low current mode and is the preferred Sleep Mode for the MC1321x. The
I/O states are maintained (the modem can be held reset), RAM and register contents are retained,
exit can be done with any active interrupt, RTI can be used with the external clock (use and external
crystal or the modem CLKO), and interrupts are serviced not treated as a reset, i.e., the normal
interrupt vector is used to generate an interrupt service routine. The only real disadvantage is that
current is slightly higher than Stop2
• Wait - In the Wait Mode the bus clock source remains active; clocks are disabled to the CPU but
peripherals can be clocked. The advantages are that current is reduced from Run Mode (useful for
short “wait” periods) and there is no stop recovery time. This state is also useful for low noise
operation when sampling the ADC. The real disadvantage is the increased current consumption
over the stop modes. Wait is not suggested for node “sleep” operation, but typically is used for
waiting for a peripheral to complete an operation
NOTE
All unused GPIO (including signals not pinned-out) must be initialized for
low power operation. If this caution is not addressed cited low power
currents may not be valid.
Table 3-9. MC1321x MCU Low Power States
Mode
Current
(typ @ 3.0V)
Advantages Disadvantages Comment
Stop1 25 nA NOT USABLE. Digital I/O
do not retain their states NOT USABLE. MCU has no means
to insure Off state of modem.
Stop2 550 nA Very low power. RAM contents
maintained. I/O states retained.
RTI can be used to wake up MCU
w/o external clock. RTI cannot use external
oscillator (poor accuracy).
Registers have to be
restored after exit.
Interrupts not serviced,
treated as a reset. Can exit with MCU reset or wake-up
timer (RTI). Can maintain M_RST
low state.