8 Electrical Connections
RS232 Serial Port
The modem supports a standard RS232 serial
interface (EIA/TIA 574) via its 9 pin Sub-D
connector, shown below.
Link the GM29 to a microcontroller or
computer in the host application, via the RS232
serial port. AT commands are used by the
host-application software to communicate with
the GM29.
Sub-D 9-pin Connector
Signal Voltage
levels
Description
DCD >+4V
<–4V
Data carrier detect
RD > +4V
<–4V
Received data
TD >2V
<0.8V
Transmitted data
DTR > 2V
<0.8V
Data terminal ready
GND 0V ground connection
DSR > +4V
<–4V
Data set ready
RTS >2V
<0.8V
Request to send
CTS > +4V
<–4V
Clear to send
RI >+4V
<–4V
Ring indicator
9
1 DCD
2RD
3TD
4 DTR
5GND
6 DSR
7RTS
8 CTS
9RI
76
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8
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