Turning The Wireless Cpu Off - Wavecom GR64 GSM/GPRS Integrator's Manual

5.8.2

Turning the Wireless CPU Off

Figure 14: Power Off timing
WARNING
Powering the GR64 power down sequence is shown above. The significant signals are
VCC, ON/OFF and VREF, shown by solid lines. The other signals (in dashed lines) are
internal to the Wireless CPU and are shown for reference purposes only.
With the Wireless CPU powered normally, ON/OFF is pulled-up to VCC potential. In
order to power down the Wireless CPU, ON/OFF is pulled to ground. Once ON/OFF
has been held low for at least 125ms the shut-down procedure begins. Although
ON/OFF can be held low for longer time, it will only delay completion of the shut-
down event. If the Wireless CPU is registered on a GSM network, the de-registration
process will complete; this may last between 3 to 30 seconds.
(PWR_KEEP) is released and approximately 70ms later the LDO outputs fall, unless
ON/OFF is held in which case the LDO's will be kept active until ON/OFF is released.
For Wireless CPU variants where VREF is an output, the absence of VREF is a useful
indicator that the networks de-registration and shut-down is complete. Once VREF is
no longer present, the application can safely remove VCC.
GR64 Integrators Manual
Page: 49/104
Failure to implement the proper shut down procedure could result in
!
permanent damage to the device including, but not limited to, erasure
of critical parameters stored in non-volatile memory. Product warranty
is invalidated in such circumstances.
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The power latch