User's Manual

Company Confidential 14 Raveon Technologies
4.3 EIA-485/RS-485 Serial I/O
RS-485 Connector Pin Out
With the RS-485 enabled (ATIO 2 command), the 9-pin serial I/O connector
on the front of the M7-UC 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 M7-UC 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 M7-UC’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 M7-UC 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.