Serial Interfaces - SimCom SIM900B Hardware Design

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Figure 12: RTC supply from non-chargeable battery
Rechargeable battery backup
Figure 13: RTC supply from rechargeable battery
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 14: Seiko XH414H-IV01E Charge-Discharge Characteristic
3.6

Serial Interfaces

SIM900B 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).
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SIM900B_Hardware Design_V2.01 2012-05-07