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SIM800C_Hardware_Design_V1.02 28 2015-4-27
Pin Min Typ Max Unit
USB_VBUS 4.3 5.0 7.0 V
4.5.4 Software Upgrade
Customer could upgrade module’s firmware through USB or UART interface.
If upgrading through USB interface, it is necessary to power on SIM800C first, and then connect USB_VBUS,
USB_DP, USB_DN, and GND to PC. There is no need to operate PWRKEY pin in the whole procedure, when
SIM800C detects USB_VBUS and could communicate normally with USB_DP and USB_DN, it will enter USB
download mode automatically.
If customer upgrades the software through UART interface, it is strongly recommended to lead the UART1_TXD,
UART1_RXD, GND and PWRKEY pin to IO connector for the upgrading, and PWRKEY pin should connect to
GND while upgrading. Refer to the following figure for debugging and upgrading software.
UART1_TXD
M odule(D C E)
UART1_RXD
GND
PW RKEY
TXD
RXD
GND
Serial P o rt
PW RKEY
I/O C onnector
Figure 24: Connection for software upgrading and debugging
The UART interface supports the CMOS level. If customer connects the module to the computer, the level shifter
should be added between the DCE and DTE.
4.6. UART1_RI Behaviors
Table 11: RI behaviors
State RI response
Standby High
Voice call
The pin is changed to low. When any of the following events occur, the pin will be changed to
high:
（1）Establish the call
（2）Hang up the call
SMS
The pin is changed to low, and kept low for 120ms when a SMS is received. Then it is changed
to high.
Others For more details, please refer to document [2].
The behavior of the RI pin is shown in the following figure when the module is used as a receiver.
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