5-6
5.1.4 Communications support devices
This section describes the devices required for connecting the inverter to a PC having no RS-485
interface or for connecting two or more inverters in multi-drop network.
5.1.4.1 Converters
Usually PCs are not equipped with an RS-485 communications port. Therefore, it is necessary to use
an RS-232C–RS-485
converter or a USB–RS-485 converter. To run the loader correctly, use a
converter satisfying the recommended specifications given below. If you use a converter other than a
recommended one, the loader may not operate properly.
Recommended converter specifications
Send/receive switching:
Auto-switching by monitoring of send/receive data status at the PC
(RS-232C)
Electric isolation: Electrically isolated from the RS-485 port
Fail-safe: Fail-safe facility*
Other requirements: Superior noise immunity
* The fail-safe facility refers to a feature that ensures the RS-485 receiver's output at "High" logic
even if the RS-485 receiver's input is opened or short-circuited or all the RS-485 drivers are
inactive. Refer to Figure 5.3 Communications Level Conversion.
Recommended converter
System Sacom Sales Corporation: KS-485PTI (RS-232C - RS-485 converter)
: USB-485I RJ45-T4P (USB - RS-485 converter)
Send/receive switching system
The RS-485 communications system of the inverter acts in half-duplex mode (2-wire) so the
converter must feature a send/receive switching circuit. Generally, the switching system may be
either one of the following.
(1) Auto-switching by monitoring of send/receive data
(2) Switching by RS-232C control signal of RTS or DTR (hardware flow control system)
FRENIC-VG
RS-232C－RS-485 変換器
RS-485
RS-232C
送受信切換
Figure 5.3 Communications Level Conversion
Driver
enable
Driver
enable
Driver
enable
Computer
Level conversion
Driver
Driver
Receiver
Receiver
Receiver output
Receiver output
Receiver input
Receiver input
Send/receive
switching
FRENIC-VG (2-wire type)
converter
Driver
enable
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