5.1 Standard RS-485 Communications Ports
5-5
Chap. 5 USING STANDARD RS-485
(2) Connection with a 4-wire type host device
Although the cables used with the converter are 2-wire types, some host devices use 4-wire type
cables. When connecting to such a host device, it is necessary to change to a 2-wire type connection
by connecting the driver output on the host device side with the receiver input using transition
wiring.
Fig 5.2 Connection with a 4-wire type host device
• The driver circuit on the host device side requires a function to change the output to high
impedance (driver enable: OFF). Always check that products using the RS-485 protocol
have this function.
• The output of the driver circuit on the host device side should be changed to high
impedance (driver enable: OFF), except during transmission.
• During host device transmission, disable the host device receiver circuit (receive
enable: OFF) so that you don’t receive back the data that you sent. If it is not possible to
disable the host device receiver circuit, program the system to discard the data you sent.
Driver
Driver
Driver
enable
Driver
enable
Receiver
enable
Receiver
enable
Receiver
Receiver
Transition
wiring
FRENIC series (2-wire type)
4-wire type host device
(master)
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