Serial Interfaces - SimCom SIM900D Hardware Design

Coin-type rechargeable battery is recommended, such as XH414H-IV01E form Seiko can be used.
Typical charge-discharge curves for this battery are shown in the following figure.
Figure 20: Seiko XH414H-IV01E Charge-Discharge Characteristic
4.6

Serial Interfaces

SIM900D provides two unbalanced asynchronous serial ports. One is the serial port and the other is the debug
port. The module is designed as a DCE (Data Communication Equipment). The following figure shows the
connection between module and client (DTE).
SIM900D_Hardware Design_V2.02
Figure 19: RTC supply from rechargeable battery
MODULE (DCE)
Serial port
TXD
RXD
RTS
CTS
DTR
DCD
RI
Debug port
DBG_TX
DBG_RX
Figure 21: Connection of the serial interfaces
CUSTOMER (DTE)
Serial port1
TXD
RXD
RTS
CTS
DTR
DCD
RING
Serial port2
TXD
RXD
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Smart Machine Smart Decision
2012-05-07