Rtc Backup - SimCom SIM802 HD Manual

SIM802 Hardware Design
Ghost mode Disconnect
(Charge-only charger
mode)
Charging in AT+CPOWD
normal mode → "Ghost
mode", then
disconnect
charger
Alarm mode Use
PWRKEY
Pin or wait
module
switch off
automatically

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
AT+CPOWD or
using PWRKEY
No direct
transition, but
via "Charging
in normal"
mode
Disconnect Switch off
the charger module by
AT+CPOWD or
using PWRKEY
Use No transition
AT+CFUN
39
Turn on the module
using PWRKEY OR
SET AT Command
"AT+CFUN=1"
Use AT+CFUN let
module enter Normal
mode, then connect
the charger to VCHG
Pin of module
12.01.2010
timer expire,
the module
turn on and
enter Alarm
mode
Set alarm by
"AT+CALAR
M", when the
timer expire,
module will
enter Alarm
mode
No direct
transition