Smart Machine Smart Decision
SIM800_Hardware Design_V1.10
28
2018-08-13
Non-chargeable battery backup
RTC
Core
1.5K
Module
VRTC
Non-chargeable
Backup Battery
Figure 17: RTC supply from non-chargeable battery
Rechargeable battery backup
RTC
Core
1.5K
Module
VRTC
Rechargeable
Backup Battery
Figure 18: RTC supply from rechargeable battery
Note: RTC can not be directly connected to the VBAT, VRTC refer to table 44.
4.5.
Serial Port and USB Interface
SIM800 provides one unbalanced asynchronous serial port. The module is designed as a DCE (Data
Communication Equipment). The following figure shows the connection between module and client (DTE).
Table 8: Serial port and USB pin definition
Name
Pin number
Function
Serial Port
DTR
3
Data terminal ready
RI
4
Ring indicator
DCD
5
Data carrier detect
CTS
7
Clear to send
RTS
8
Request to send
TXD
9
Transmit data
RXD
10
Receive data
USB Interface
USB_VBUS
24
USB power supply
USB_DP
27
USB data line positive
USB_DN
28
USB data line negative
