Function Of Serial Port And Debug Port - SimCom SIM900B Hardware Design

If only RXD and TXD are used in user's application, other serial pins should be kept open. Please refer to
following figure.
Note: if sleep mode is need in this situation, the user nees to connect the DTR signal as well, or only sleep mode2 can be used.
For details, please refer to document [7].
3.6.1

Function of Serial Port and Debug Port

Serial port:
Full modem device.
Contains data lines TXD and RXD, hardware flow control lines RTS and CTS, status lines DTR, DCD and
RI.
Serial port can be used for CSD FAX, GPRS service and AT communication. It can also be used for
multiplexing function. For details about multiplexing function, please refer to document [7].
Serial port supports the following baud rates:
1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200bps
Autobauding only supports the following baud rates:
1200, 2400, 4800, 9600, 19200, 38400 and 57600bps
The default setting is autobauding.
SIM900B_Hardware Design_V2.01
MODULE (DCE)
Serial port
TXD
RXD
RTS
CTS
DTR
DCD
RI
Debug port
DBG_TX
DBG_RX
Figure 15: Connection of the serial interfaces
MODULE (DCE)
Serial port
TXD
RXD
RTS
CTS
DTR
DCD
RI
Debug port
DBG_TX
DBG_RX
Figure 16: Connection of RXD and TXD only
CUSTOMER (DTE)
Serial port1
TXD
RXD
RTS
CTS
DTR
DCD
RING
Serial port2
TXD
RXD
CUSTOMER (DTE)
Serial port1
TXD
RXD
RTS
CTS
DTR
DCD
RING
Serial port2
TXD
RXD
22
Smart Machine Smart Decision
2012-05-07