Smart Machine Smart Decision
SIM800C_Hardware_Design_V1.02
24
2015-4-27
R T C
C ore
1.5K
M odule
V R T C
N on-chargeable
B ackup B attery
Figure 16: RTC supply from non-chargeable battery
Rechargeable battery backup
R T C
C ore
1.5K
M odule
V R T C
R echargeable
B ackup B attery
Figure 17: RTC supply from rechargeable battery
Note: When shut off VBAT and power on VRTC only, the clock error becomes larger.
4.5.
Serial Port and USB Interface
SIM800C default provides one unbalanced asynchronous serial ports. 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
Note: Hardware flow control is disabled by default. AT command “AT+IFC=2, 2”can enable hardware flow
Pin name
Pin number
Function
UART1_DTR
6
Data terminal ready
UART1_RI
7
Ring indicator
UART1_DCD
5
Data carrier detect
UART1_CTS
4
Clear to send
UART1_RTS
3
Request to send
UART1_TXD
1
Transmit data
UART1_RXD
2
Receive data
UART2_TXD
22
Transmit data
Serial port
UART2_RXD
23
Receive data
USB_VBUS
24
USB power supply
USB_DP
25
D+ data input/output
Debug port
USB_DN
26
D- data input/output
