GSM/GPRS Module Series
M85 Hardware Design
M85_Hardware_Design Confidential / Released 31 / 88
K2
EMERG_OFF
TVS2
Close to K2
Figure 11: 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 shut down 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 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
The module can be restarted by driving the PWRKEY to a low level voltage for a certain time, which is
similar to the way of turning on module. In order to make the internal LDOs discharge completely after
turning off the module, it is recommended to delay about 500ms before restarting the module. The restart
timing is illustrated as the following figure.
PWRKEY
(INPUT)
STATUS
(OUTPUT)
Delay >500ms
Turn off
Restart
Pull down the PWRKEY
to turn on the module
Figure 12: Timing of Restarting System
