Motorola W24, Technical Information

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Power On/Off Operation
12 Module Hardware Description May 31, 2008
Power On/Off Operation
The W24 power on consists of two primary phases:
Initial power up is hardware controlled by the Power-up/down circuit which monitors two
power-up control signals: ON_N and IGN. If any of these two signals is asserted, the
Power-up/down circuit will enable Voltage regulators and the power management IC. They will
provide valid supply voltages to the processor which will start to boot.
The second phase is SW controlled. Processor checks the state of ON_N and IGN signals and if
any of them is asserted, the CPU takes control over the voltage regulators and power management
IC and holds them enabled.
Power down is controlled by SW - Once valid power-down condition occurs, CPU will release
the signal which keeps the regulators and power management enabled, thus causing the W24 to
power down. If this happened while IGN signal is still asserted, the regulators will remain active,
and the unit will enter "Off mode".
W24 state is indicated at the interface connector by the hardware output signals RESET_N. The
RESET_N signal indicates whether W24 is powered on or off. When the RESET_N is low, W24
is powered-off. When it is high, W24 is powered-on.
Note:
As the power down process in W24 is SW controlled, if an unexpected reset occurs, the
module will power down if it is not being held by the IGN signal. Therefore, although
both ways of powering up/down are provided to user, we recommend using IGN as a sole
power up/down control signal. By using IGN as a control signal, user insures that in case
of an unexpected reset, the unit automatically turns on. If the IGN was not asserted, the
unit will remain "OFF" after a reset.
Important:
Do not operate the W24 out of its electrical or environmental limits. Refer to the
specifications chapter for details of these limits.
Turning the W24 On
When the W24 power supply is stable above the minimum operating level and W24 is powered
off, all of its circuits are disabled.
When W24 is turned on, by any of the methods described below, it will first perform an automatic
initialization. When the initialization has completed, W24 resumes normal operation (stand alone
mode), or turns on the G24 module (stacked modules) and resumes normal operation.
During the internal system-test process W24 may toggle several interface signals, which are
visible to the application. These signals do not represent any valid state or data, and should be
ignored by the customer application until the system-test has completed.
Valid Turn-on reasons are:
•
ON_N asserted low for 0.5s
•
IGNITION asserted
Note:
During FW upgrades (reflashing) make sure to power-up the W24 by IGN.