Specifications

4.4. EIA-485/RS-485 Serial I/O (Optional)
RS-485 Connector Pin Out
With the RS-485 option installed, the 9-pin serial I/O connector on the front of
the FireLine is a female 9-p D-subminiature connector having the following
pins configuration.
Front-view of DB-9 connector on modem (female)
Pin # Name Dir Function Level / Specification
1
- Do not connect Do not connect this pin to anything.
2
- Do not connect Do not connect this pin to anything.
3
B (-)
I/O B Inverting RS-485 line
4
A (+)
I/O A Non-inverting RS-485 line
5
GND Ground Connect to earth ground.
6
- Do not connect Do not connect this pin to anything.
7
Out +
out
Do not connect Internal connection to pin 4
8
In -
in
Do not connect Internal connection to pin 3
9
Vin
In/Out
DC Power
DC Power in or out if unit is powered using DC in
jack.
The RS485 differential line consists of two pins, A and B.
A TxD-/RxD- aka inverting pin which is negative (compared to B) when the
line is idle.
B TxD+/RxD+ aka non-inverting pin which is positive (compared to A)
when the line is idle.
Configuring
To configure the FireLine modem for RS-485 operation, use the ATIO x
command. ATIO 2 sets the serial port for standard RS-485, full duplex. ATIO
3 sets the serial port for RS-485 simplex mode. In most cases, simplex is
preferred (ATIO 3 ). In simplex RS-485 mode, the FireLine’s serial data
receiver is internally disabled whenever it sends a character out the serial
port, so that it will not receive its own data. You must order the RS-485
option for this to work, and only modems with Revision E or higher hardware
can work in RS-485 mode. For most application use the RS485 simplex
mode, ATIO 3. If you are using two FireLine modems with RS485 on both
units, you must use the simplex RS485 mode instead of the duplex RS485
mode, or the modems will enter an infinite loop-back condition.
Raveon’s RS-485 I/O circuit uses 3.3V logic to drive the lines, and the RS485
pins are ESD protected to ±15kV and 7kV human body model . Input current
is less than 150uA. Output current when not driving the line is less than
50uA.