M20 Hardware Design
If the voltage
≤
3.4V, the following URC will be presented:
UNDER-VOLTAGE POWER DOWN
If the voltage
≥
4.6V, the following URC will be presented:
OVER-VOLTAGE POWER DOWN
After this moment, no further AT command can be executed. The module logoff from network and
enters POWER DOWN mode, and only RTC is still active. The POWER DOWN mode can also
be indicated by the pin VDD_EXT, which is a low level voltage in this mode.
3.4.2.4 Emergency shutdown
The module can be shut down by driving the pin EMERG_OFF to a low level voltage for over
20ms and then releasing it. The EMERG_OFF line can be driven by an Open Drain/Collector
driver or a button. The circuit illustrates as the following figures.
4.7K
47K
Emergency
shutdown impulse
EMERG_OFF
Figure 9: Reference circuit for EMERG_OFF by
using driving circuit
S1
EMERG_OFF
TVS1
Close to S1
Figure 10: Reference circuit for EMERG_OFF
by using button
Be cautious to use the pin EMERG_OFF. It should only be used under emergent situation. For
instance, if the module is unresponsive or abnormal, the pin EMERG_OFF could be used to
M20_HD_V1.01
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