Smart Machine Smart Decision
SIM868_Series_Hardware_Design_V1.06
33
2017-07-13
Table 11: USB_VBUS operation voltage
Pin
Min
Typ
Max
Unit
USB_VBUS
4.3
5.0
7.0
V
5.5.4.
Software Upgrade of GSM
Customer could upgrade module’s GSM part firmware through USB or UART interface.
If upgrading GSM part through USB interface, it is necessary to connect USB_VBUS, USB_DP, USB_DM, and
GND to PC. There is no need to operate PWRKEY pin in the whole procedure, when GSM detects USB_VBUS
and can communicate normally with USB_DP and USB_DM, it will enter USB download mode automatically.
If customer upgrades GSM 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 be
connected to GND while upgrading. Refer to Figure 24 for debugging and upgrading software.
UART1_TXD
GSM(DCE)
UART1_RXD
GND
PWRKEY
TXD
RXD
GND
Serial Port
PWRKEY
I/O Connector
Figure 24: Connection for software upgrading
The UART interface supports the CMOS level. If customer connects the module to the computer, the level shift
should be added between the DCE and DTE.
5.6.
UART1_RI Behaviors
Table 12: UART_RI behaviours
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].
SIMCOM
CONFIDENTIAL
FILE
