28 SBC-410 User's Manual
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 printer) but was later adopted
by the 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
Ground <
5
Ground
6
RTS-
>
9
CTS-
7
RTS+
>
8
CTS+
8
CTS+ <
7
RTS+
9
CTS- <
6
RTS-
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.
Computer A
Device B
Pin
Signal
Pin
Signal
1
TX-
Data-
1
TX-
4
RX-
4
RX-
2
TX+
2
TX+
3
RX+
Data+
3
RX+
5
Ground
5
Ground
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