SIM900D Hardware Design
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DBG_RXD: Receive data from the TXD signal line of the DTE
The logic levels are described in following table.
Table12: Logic levels of the serial port and debug port
Parameter
Min
Max
Unit
V
IL
0
0.4
V
V
IH
2.4
3
V
V
OL
0
0.1
V
V
OH
2.7
3
V
TXD
RXD
RTS
CTS
DTR
DCD
RI
TXD
RXD
RTS
CTS
DTR
DCD
RING
DBG_TX
DBG_RX
MODULE (DCE)
CUSTOMER (DTE)
Serial port1
Serial port
Debug port
Serial port2
TXD
RXD
Figure18: Connection
of the serial interfaces
3.9.1 Function of serial port & debug port supporting
Serial port
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Modem device.
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Contains data lines TXD and RXD, State lines RTS and CTS, Control lines DTR, DCD and RI.
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Serial port can be used for CSD FAX, GPRS service and send AT command of controlling module. Also
serial port can be used for multiplexing function. SIM900D supports only basic mode of multiplexing so far.
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Serial port supports the communication rates as following:
1200,2400, 4800, 9600, 19200, 38400, 57600, 115200bps
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Autobauding supports baud rates as following:
1200, 2400, 4800, 9600, 19200, 38400, and 57600bps, the default setting is autobauding.
Autobauding allows the GSM engine to automatically detect the baud rate configured in the host application. The
serial port of the GSM engine supports autobauding for the following baud rates: 1200, 2400, 4800, 9600, 19200,
SIM900D_Hardware Design_V1.04
2010.10.09
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