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Modem Modes of Operation
MC1321x Reference Manual, Rev. 1.0
7-4
Freescale Semiconductor
7.2
Low Power Modes
The MC1321x supports several low-power modes where the transceiver circuitry is not active. Each mode
has a different advantage, these modes are described in the following sections.
7.2.1
Off Mode
The Off or Reset condition has the absolutely lowest power, and is controlled by the RST input. As long
as RST is asserted low the MC1321x remains in the Off Mode. All functions are disabled and no RAM
data is retained. Current draw is attributed to leakage only.
To exit Off Mode, RST is negated high. The MC1321x then moves to Idle Mode within 25 milliseconds.
7.2.2
Hibernate Mode
Although the Off or Reset condition has the lowest possible power, the Hibernate Mode has the next lowest
power. All hardware blocks are deactivated (including the SPI interface) and no timers are running.
Internal voltage regulation is dropped to less than 1 Vdc. Hibernate Mode has the advantage of retention
of all RAM data (which does not occur in the Off Mode) and of the SPI configuration prior to entering
Hibernate Mode.
Hibernate Mode is entered from Idle by programming hib_en, Control_B Register 07, Bit 1, to “1”.
Hibernate is then entered 128 CLKO cycles after hib_en is set. The normal way to exit from Hibernate
Mode is to assert ATTN which will cause the MC1321x to go to Idle Mode. The MC1321x then moves to
Idle Mode within 20 milliseconds. Asserting RST which will force the Off condition.
On entering Hibernate Mode, 128 clock cycles are available at CLKO before the clock is disabled. These
128 CLKO cycles allow a host that uses CLKO as a source clock to attain a low power state prior to losing
clock. After the 128 CLKO cycles, the transceiver transitions to the low power state.
Upon exiting Hibernate, CLKO will restart (if enabled) with the same frequency as programmed before
before entering Hibernate.
7.2.3
Doze Mode
Doze Mode has variations of normal Doze Mode and a subset called Acoma state.
7.2.3.1
Normal Doze Mode
Doze Mode is an additional low power state specifically designed to work in concert with the Event Timer.
Most internal hardware blocks are de-activated (including the SPI interface) and internal regulation is
reduced, but the reference oscillator and Event Timer are active. Internal RAM data and SPI configuration
are retained similar to Hibernate Mode.
In Doze Mode, CLKO can optionally be made available by setting clko_doze_en, Control_B Register 07,
Bit 9, with the disadvantage of increased power consumption. The CLKO frequency must be set for 1 MHz
or lower. If clko_doze_en = 0, then CLKO is disabled 128 clock cycles after entering Doze Mode.