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RS232 SERIAL COMMUNICATION
RS485 SERIAL COMMUNICATION
If the RS485 network exceeds 100 metres in length or baud-rate over 9600 are
used, two terminating resistors are needed at the ends of the network. Two
120 ohm resistors must be connected between the “+” and “–” terminals of the
line, on the terminal strip of the furthest instruments. Should there be different
instruments or converters, refer to the specific manuals to determine whether it is
necessary to connect the above-mentioned resistors.
DIRECT CONNECTION BETWEEN RS485 AND RS232 WITHOUT CONVERTER
Since a two-wire RS485 output may be used directly on the RS-232 input of a PC or remote display,
it is possible to implement instrument connection to an RS-232 port in the following manner:
INSTRUMENT RS232
RS485 – → RXD
RS485 + → GND
This type of connection allows A SINGLE instrument to be used in a ONE WAY
mode.
DB9-F
5
3
2
INSTRUMENT
RS232 TXD
PC
RS232 RXD
GND
INSTRUMENT
RS485 +
RS485 -
max 500 m
RS485 +
3 2 5
PC RS232
RX+
RX-
TX-
TX+
CONVLAU
24 VDC
+
-
0
TX
RX
VIN
RS485 +
RS485 -
RS485 -
RS485 +
RS485 -
RS485 +
RS485 -
GND
GND
GND
INSTRUMENT INSTRUMENT
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