User I/O Connector
The User I/O is via a female 9-p D-subminiature connector. The following
pins are defined.
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. 0
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.
3
TxD
in
Transmit data
Data in.
4
DTR
in
Data terminal ready Normally ignored by the
FireLine
modem. If
SLEEP mode is enabled, this line will put
modem to sleep if negated, or active mode
if it is asserted.
5
GND
Ground connection
Signal and power ground
6
DSR
out
Data Set Ready
Normally is set to 0 when modem is
powered on.
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.
8
CTS
out
Clear to send
Used to stop the flow of data coming into
the RxD pin from the device connected to
the
FireLine
. 0 = OK to send, 1 = don’t
send.
9
Power
In/out DC power (not Ring
signal)
User may supple 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 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.
