Smart Machine Smart Decision
TXD
RXD
RTS
CTS
DTR
DCD
RI
TXD
RXD
RTS
CTS
DTR
DCD
RING
MODULE (DCE)
CUSTOMER (DTE)
Serial port1
Serial port
Debug port
Serial port2
DBG_RX
DBG_TX
TXD
RXD
Figure 19: Connection of RXD and TXD only
4.5.1
Function of Serial Port and Debug Port
Serial port:
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Full modem device.
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Contains data lines TXD and RXD, hardware flow control lines RTS and CTS, status lines DTR, DCD and
RI.
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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 [3]
.
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Serial port supports the following baud rates:
600, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600, 115200, 230400 and 460800bps
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Autobauding only supports the following baud rates:
600, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600 and 115200bps
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The default setting is autobauding.
Autobauding allows SIM900-DS to automatically detect the baud rate of the host device. Pay more attention to
the following requirements:
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Synchronization between DTE and DCE:
When DCE powers on with autobauding enabled, user must firstly send character “A” to synchronize the
baud rate. It is recommended to send “AT” until DTE receives the “OK” response, which means DTE and
DCE are correctly synchronized. For more information please refer to the AT command “AT+IPR”.
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Restrictions of autobauding operation:
The DTE serial port must be set at 8 data bits, no parity and 1 stop bit.
The URC such as "RDY", "+CFUN: 1" and "+CPIN: READY” will not be reported.
Note: User can use AT command “AT+IPR=x” to set a fixed baud rate and the setting will be saved to non-volatile flash
memory automatically. After the configuration is set as fixed baud rate, the URC such as "RDY", "+CFUN: 1" and "+CPIN:
READY” will be reported when SIM900-DS is powered on.
Debug port:
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Used for debugging and upgrading firmware.
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Debug port supports the baud rate of 115200bps.
SIM900-DS_Hardware Design_V1.00
25
2013-01-20
