Sim800 hardware design v1.05

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4.5.4 Software Upgrade and Debug
USB and UART interfaces can be used for firmware upgrade.
If customer upgrading firmware via the USB port, SIM800 must be powered first, then connect VBUS, USB_DP,
USB_DM and GND to PC. There is no need to operate PWRKEY pin in the whole procedure, when SIM800
detects VBUS and could communicate normally by USB_DP and USB_DM, module will enter USB download
mode automatically.
Note: When only USB_DP and USB_DM connected, no VBUS, customer need to pull down COL0 before
power on the module, then press the PWRKEY button, the module will enter download mode;
If customer upgrading firmware via the UART port, it is strongly recommended that reserve the
UART_TXD,UART_RXD,GND and PWRKEY pins to IO connector for the upgrade, and PWRKEY pin should
connect to GND while upgrading. Refer to the following figure for upgrading software.
Figure 25: Connection for software upgrading
The serial port supports the CMOS level. If user connects the module to the computer, the level shifter should be
added between the DCE and DTE.
4.5.5 Multiplex Function of Serial Port
If full modem function is not used, the UART port could be configured to two serial ports without flow control,
the details could be founded in the following table:
Table 11: Multiplex function of serial port
Name Pin Mode 0(default) Mode 1
UART_DTR 3 UART_DTR GPIO22
UART_RI 4 UART_RI GPIO23
UART_DCD 5 UART_DCD GPIO24
CTS 7 CTS URXD2(IN)
RTS 8 RTS UTXD2(OUT)
SIM800_Hardware Design_V1.05 33 2014-03-25