SIM802 Hardware Design
one analog GND pins are recommended for grounding. The VCHG Pin serves as a control signal
for charging a Li-Ion battery. VRTC Pin can be used to back up the RTC.
3.3.2 Minimizing power losses
Please pay special attention to the supply power when you are designing your applications. Please
make sure that the input voltage will never drop below 3.4V even in a transmitting burst during
which the current consumption may rise up to 2A. If the power voltage drops below 3.4V, the
module may be switched off. You should also take the resistance from the power supply lines on
the host board or from battery pack into account.
3.3.3 Monitoring power supply
To monitor the supply voltage, you can use the “AT+CBC” command which include three
parameters: charging state, voltage percentage and voltage value (in mV). It returns charge state
，
the battery voltage 1-100 percent of capacity and actual value measured at VBAT and GND.
The voltage is continuously measured at intervals depending on the operating mode. The
displayed voltage (in mV) is averaged over the last measuring period before the AT+CBC
command is executed.
For details please refer to
document [1]
3.4 Power up/down scenarios
3.4.1 Turn on SIM802
SIM802 can be turned on by various ways, which are described in following chapters:
z
Via PWRKEY Pin: starts normal operating mode (see chapter 3.2);
z
Via VCHG Pin: starts GHOST modes (see chapter 3.4.1.2);
z
Via RTC interrupt: starts ALARM modes (see chapter 3.4.1.4)
Note: The AT command must be set after the SIM802 is power on and Unsolicited Result Code
“RDY” is received from the serial port. However if the SIM802 is set autobauding, the serial
port will receive nothing. The AT commands can be set in 2-3s after the SIM802 is power on.
You can use AT+IPR=x;&W to set a fixed baud rate and save the configuration to non-volatile
flash memory. After the configuration is saved as fixed baud rate, the Code “RDY” should be
received from the serial port all the time that the SIM802 is power on. Please refer to the
chapter AT+IPR in document [1].
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