Data Sheet

Smart Machine Smart Decision
SIM800F_Hardware Design_V1.00 33 2015-07-31
If upgrading through USB interface, it is necessary to power on SIM800F 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
SIM800F detects USB_VBUS and could communicate with USB_DP and USB_DN, it will enter USB download
mode automatically.
If users upgrade the software through UART interface, it is 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. The reference connection is shown as below:
Figure 26: Connection for software upgrading and debugging through UART
UART interface does not support RS-232 level. When connect the module to the computer, the level shifter is
needed.
For more details about software upgrading, please refer to document
[4]
.
4.7 RI Behaviors
Table 11: RI Behaviors
State RI response
Standby High
Receive
Voice call
Changed to low. But when any of the following events occur, it will be changed to high:
（1）Establish the call
（2）Hang up the call
Receive
SMS
Changed to low, and kept low for 120ms, then changed to high.
URC
When URC are reported, this pin will be changed to low, and kept low for 120ms, then changed to
high. For more details, please refer to document
[8]
.
The behavior of the RI pin is shown in the following figure when the module is used as a receiver.