SIM802 Hardware Design
AT+CPOWD or
using PWRKEY
timer expire,
the module
turn on and
enter Alarm
mode
Ghost mode
(Charge-only
mode)
Disconnect
charger
No direct
transition, but
via “Charging
in normal”
mode
Turn on the module
using PWRKEY OR
SET AT Command
“AT+CFUN=1”
Set alarm by
“AT+CALAR
M”, when the
timer expire,
module will
enter Alarm
mode
Charging in
normal mode
AT+CPOWD
→
“Ghost
mode”, then
disconnect
charger
Disconnect
the charger
Switch off
module by
AT+CPOWD or
using PWRKEY
No direct
transition
Alarm mode
Use
PWRKEY
Pin or wait
module
switch off
automatically
Use
AT+CFUN
No transition
Use AT+CFUN let
module enter Normal
mode, then connect
the charger to VCHG
Pin of module
3.8 RTC backup
The RTC (Real Time Clock) power supply of module can be provided by an external battery or a
battery (rechargeable or non-chargeable) through VRTC Pin. There is a 10K resistance which has
been integrated in SIM802 module used for limiting current. You need only a coin-cell battery or
a super-cap to VRTC Pin to backup power supply for RTC.
The following figures show various sample circuits for RTC backup.
SIM802_HD_V2.01
12.01.2010
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