M20 Hardware Design
shutdown the system. Although turning off the module by EMERG_OFF is fully tested and
nothing wrong detected, this operation is still a big risk as it could cause destroying of the code or
data area of the NOR flash memory in the module. Therefore, it is recommended that PWRKEY
or AT command should always be the preferential way to turn off the system.
3.4.3 Restart module using the PWRKEY pin
Customer’s application can restart the module by driving the PWRKEY to a low level voltage for
certain time, which is similar to the way to turn on module. Before restarting the module, at least
500ms should be delayed after detecting the low level of VDD_EXT. The restart scenario
illustrates as the following figure.
VDD_EXT
（
OUTPUT
）
H
PWRKEY
（
INPUT
）
V
IL
<0.3*VDD_EXT
Delay > 500ms
Turn off
Pull down the PWRKEY
to turn on the module
Restart
Figure 11: Timing of restart the system
The module can also be restarted by the PWRKEY after emergency shutdown.
PWRKEY
（
INPUT
）
Pulldown > 20ms
Delay>2s
EMERG_OFF
（
INPUT
）
Figure 12: Timing of restart the system after emergency shutdown
M20_HD_V1.01
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