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Pinout Descriptions
Pin Signal In/Out Description
24
-Reset
I
Device Reset (with pull-up). The active low -RESET input resets the device logic
and returns the configuration of the device to the original factory default values or
"stored values" in the NVRAM. -RESET is tied to VCC through a time-constant
circuit for "Power-on-Reset" functionality. The module is ready to accept commands
after about 6 seconds after power-on or reset.
This signal is used to force a reset procedure by providing low level during reset of
at least 500µs. The signal is considered an emergency reset only. A reset
procedure is already driven by internal hardware during the power-up sequence. If
no external reset is necessary, this input can be left open. If used (emergency
reset), it has to be driven by an open collector or an open drain.
26
GND
I
Logic Ground.
33
-RTS
I
Request to Sent (Active Low). -RTS signal is used for hardware flow control. -RTS
input ON (low) indicates that the DTE is ready to send data to the modem. In the
command state, the modem ignores -RTS.
Note: When the -RTS pin is not in use, it should be tied low.
34
-RXD
O
Received Data. The module uses the RXD line to send data to the DTE and to
send module responses to the DTE. In command mode, -RXD data presents the
module responses to the DTE. Module responses take priority over incoming data
when the two signals are in competition for -RXD. When no data is transmitted, the
signal is held in mark condition.
35
-TXD
I
Transmitted Data. The DTE uses the -TXD line to send data to the module for
transmission or to transmit commands to the module. The DTE holds this circuit in
mark state when no data is being transmitted or during intervals between
characters.
36
-RI
O
RING (Active Low). Incoming ring signal from phone.
Ring Indicate. -RI output ON (low) indicates the presence of an ON segment of a
ring signal on the telephone line. The modem will not go off-hook when -RI is active;
the modem waits for -RI to go inactive before going off-hook.
37
-DSR
O
Data Set Ready (Active Low). -DSR indicates module status to the DTE. -DSR
OFF (high) indicates that the DTE is to disregard all signals appearing on the
interchange circuits except Ring Indicator (-RI). It reflects the status of the local data
set and does not indicate an actual link with any remote data equipment.
-CTS
O
Clear to Send (Active Low). -CTS is controlled by the module to indicate whether
38
or not the module is ready to transmit data. -CTS ON indicates to the DTE that
signals on TXD will be transmitted. -CTS OFF indicates to the DTE that it should not
transfer data on TXD.
-DCD
O
Data Carrier Detect (Active Low). -DCD output is ON (low) when a data
39
connection is established and the module is ready to send/receive data.
40
-DTR
I
Data Terminal Ready (Active Low). The -DTR input is turned ON (low) when the
DTE is ready to communicate. -DTR ON prepares the modem to be connected, and,
once connected, maintains the connection. -DTR OFF places the modem in the
disconnect state under control of the &Dn and &Qn commands.
Note: When the -DTR pin is not in use, it should be tied low.
41
GND
I
Logic Ground.
61
VCC
I
DC Input Power. 5V DC power.
63
GND
I
Analog Ground. Analog ground is tied common with DGND on the SocketModem.
To minimize potential ground noise issues, connect audio circuit return to AGND.
Multi-Tech Systems, Inc. SocketModem GSM Hardware Guide for Developers
Chapter 1 – SocketModem GSM
8
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