User's Manual

RS232/EIA232 Serial I/O Connector
The RS232 9-pin serial I/O connector is a female 9-pin D-subminiature
connector having the following pins configuration. It is pinned out so that it
may be plugged directly into a computer or PC’s 9-pin COM port.
Front-view of DB-9 connector on modem (female)
Pin Name Dir Function Level / Specification
1 CD out Carrier detect If enabled, indicates presence of carrier.
Logical 0 (+ voltage on RS-232) means carrier
is present. If disabled, it is asserted (0)
whenever the modem is operational, and not in
the configuration mode. It will be a 1 when the
modem is in the configuration mode.
2 RxD out Receive data Data out of the modem.
3 TxD in Transmit data Data into the modem.
4 DTR in Data terminal
ready
Normally ignored by the M7 modem. May
control the power-state of the modem in low-
power mode if this feature is enabled.
5 GND Ground
connection
Signal and power ground
6 DSR
out
Data Set Ready
Normally is set to 0 when modem is powered on
and running. Modem sets to a 1 when in low-
power mode.
7 RTS
in
Request to send
Used to stop/start the flow of data coming out of
the modem TxD pin. 0 = OK to send, 1 = don’t
send. Leave disconnected if not used.
8 CTS
out
Clear to send
Used to stop the flow of data going into the RxD
pin from the device connected to the M7. 0 =
OK to send, 1 = don’t send. If the M7 cannot
accept more data, it will negate this signal (set
to a 1).
9 Power
In/out DC power (not
Ring signal)
User may supply the DC power to the modem
on this pin.
Note: RS-232 signals use positive and negative voltages to represent digital 1s and 0s. A positive
voltage is a 0, and a negative voltage is a digital 1.
This pin-out allows it to be directly plugged into a computer’s 9-pin serial port
using a conventional 9-pin RS-232 serial cable. To connect it to a modem, or
computer peripheral that has a serial port, you will need a “null-modem”
cable. See Appendix A for more information on wiring a null-modem cable.
To configure the M7 modem for RS-232 operation, use the ATIO 0 command.
RS-232 is the default operation mode for the connector. RS-485 is a factory
option. See the next section for details on the RS-485 option.