RV-M7 Technical Manual
15
4.6 Optional EIA-485/RS-485 Serial I/O
RS-485 Connector Pin Out
RS-485 is a two-wire connection, with the pair of wires transmitting and receiving data. With the RS-485
enabled (
ATIO 2
command), the 9-pin serial I/O connector on the front of the M7 is a female 9-pin D-
subminiature connector having the following pins configuration.
Front-view of DB-9 connector on modem (female)
Pin #
Name
Direction
Function
Level / Specification
1
-
Do not connect
Do not connect this pin to anything.
2
B (-)
I/O
B
Inverting RS-485 data in line
3
Out -
out
Z
Connect to pin 2
4
A (+)
I/O
A
Non-inverting RS-485 data out line
5
GND
-
Ground
Connect to earth ground.
6
-
Do not connect
Do not connect this pin to anything.
7
Out +
out
Y
Connect to pin 4
8
9
Vin
In/Out
DC Power
DC Power in or out if unit is powered using DC
in jack.
The RS-485 differential line consists of two pins, A and B.
A
TxD+/RxD+ non-inverting pin which is positive (compared to B) when the line is idle.
B
TxD-/RxD- aka inverting pin which is negative (compared to A) when the line is idle.
Configuring
To configure the
M7
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, RS-
485 simplex is preferred (
ATIO 3
). In simplex RS-485 mode, the
M7
’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. For
most application use the RS-485 simplex mode,
ATIO 3
. If you are using two
M7
modems with RS-485
on both units, you must use the simplex RS-485 mode instead of the duplex RS-485 mode, or the
modems will enter an infinite loop-back condition.
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