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Smart Machine Smart DecisionBog'liq SIM800L Smart Machine Smart Decision
z External capacitor backup
RTC
Core
2.2K
VRTC
Large-capacitance
Capacitor
Figure 17: RTC supply from capacitor
z Non-chargeable battery backup
Figure 18: RTC supply from non-chargeable battery
z Rechargeable battery backup
Figure 19: RTC supply from rechargeable battery
Note: The clock error becomes larger when VBAT is turned off and RTC circuit was supplied from the backup battery or the
external capacitor.
4.5. Serial Port and USB Interface
SIM800H&SIM800L 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).
SIM800H&SIM800L_Hardware Design_V2.02 28 2015-07-27
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Table 9: Serial port and USB pin definition
Pin name
Pin number Function
DTR
69
Data terminal ready
RI
68
Ring indicator
DCD
70
Data carrier detect
CTS
34
Request to send
RTS
33
Clear to send
TXD
32
Transmit data
Serial port
RXD
31
Receive data
VBUS
7
USB power supply
USB_DP
59
Debug port
USB_DN
19
Note: Hardware flow control is disable by default. AT command “AT+IFC=2,2”can enable hardware flow control. AT command
“AT+IFC=0,0”can disable hardware flow control. For more details please refer to document [1].
Table 10: Serial port characteristics
Symbol
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