GSM UART Port Application Note
GSM_UART_Application_Note_V1.0
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6. Control Signals
6.1.
DCD
The DCD pin will be active (low) after establishing a data connection. When the data
connection is turned off, the DCD pin will go to inactive (high)
6.2.
DTR
The module would automatically go into SLEEP mode, if the DTR is set to high level, the
slow clocking mode is already enabled by AT+QSCLK, and there is no specific task for the
module to handle. In this case, the current consumption of module will reduce to the
minimal level. During the SLEEP mode, the module can still receive paging message and
SMS normally. If the DTR Pin is pulled down, the module would exit from SLEEP mode.
The UART port will be active about 600ms after the DTR is changed to low level.
DTE can use the DTR pin to control the active or inactive state of the SLEEP mode as
shown in Figure 7.
Figure 7:
DTR for waking up
In TCP/IP application (for more detail, please refer to TCP/IP application notes ), the DTR
pin can also be used to switch from data mode to command mode. To use this method,
AT&D1 should be set firstly. Depending on the state of the DTR pin, there are 2 ways to
implement this function.
1. If the DTR pin is set to low in data mode, setting it to high for about 600ms would force
the UART port from data mode to command mode.
2. If the DTR pin is set to high in data mode, pulling it to low level for about 1000ms and
then pulling it up for about 600ms would also switch the module from data mode to
command mode.
When the module successfully switches from data mode to command mode, a URC “OK”
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