22 PCA-6143P User's Manual
å
RS-422 signal wiring
RS-422 is used for long-distance point-to-point connections. RS-
422 originally used four wires for one-way communication (with
devices such as display terminals or printers) but was later
adopted by industry for simultaneous two-way communication by
doubling the number of wires.
Each pin on the first device connects to a corresponding device on
the second. Flow control lines manage the communication. The
following table shows pin connections:
Computer A
Computer B
Pin
Signal
Pin
Signal
1
TX-
>
4
RX-
2
TX+
>
3
RX+
3
RX+
<
2
TX+
4
RX-
<
1
TX-
5
GND
<
>
5
GND
6
RTS-
>
9
CTS-
7
RTS+
>
8
CTS+
8
CTS+
<
7
RTS+
9
CTS-
<
6
RTS-
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RS-485 signal wiring
In a typical RS-485 application the host device requests data from
a slave module then listens for the response. The host transmits
and receives data on the same pair of wires. Software handles the
flow control; no other wires are needed.
Pin assignments appear in the following table. Pins 1 and 4 share
the Data+ wire. Pins 2 and 3 share the Data- wire.
Data+
Data-
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