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Technical reference section
AT&Dn - Data Terminal Ready (DTR) options
AT&Dn
[n=0..3]
Option
Result
AT&D0
The GSM module ignores the status of the DTR control line connected
to the COM interface.
AT&D1
When the DTR line switches from ON to OFF , the GSM module changes
to command mode. The existing connection to the distant station is not
cleared down.
AT&D2
When the DTR line switches from ON to OFF , the GSM module sets up
a connection to the distant station, switches to command mode and
deactivates auto-answer mode. Auto-answer can be reactivated by
resetting DTR to ON.
AT&D3
The transition of DTR to OFF has the same effect as an AT&F command,
i.e. the factory configuration is loaded. An existing connection to the dis-
tant station is cleared down.
Data flow control
Even if your PC is set, for example, to 19200 baud, the maximum GSM rate that can
be used is 9600 bit/s. A higher setting causes the GSM module to receive more data
from the PC than it can transfer to the GSM network. In order to prevent a data over-
flow, it must be able to interrupt the data flow from the PC. This is accomplished by
means of the RTS/CTS hardware data flow control, which switches over the COM in-
terface so as to interrupt the RTS (computer) and CTS (GSM module) control lines.
Memory commands
The GSM module is equipped with a 128-byte nonvolatile RAM in which the values of
the modifiable S-registers and other values are stored. This section describes the val-
ues, how to store them and how to use them.
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