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Is special cabling required to control RS422 and RS485 devices from the SD4008? The SD4008 supports multiple signalling protocols (RS-232, RS-422 and RS-485) on the serial RJ-45 ports 1 through 8. For RS-422 the signalling is full duplex transmit on TX+/TX- pair, receive on RX+/RX- pair: 
For RS-485 it's half duplex - single pair - and to provide half duplex 'party-line' communications over a 2-wire bus (D+/D-), two short cable loops are required between the RX+/TX+ pins (pins 2 and 5) and RX-/TX- pins (pins 4 and 7) on the serial RJ-45 cable connector.  This is because the SD4008 uses universal differential transceivers that support 4-wire (RS-422) and 2-wire (RS-485) operation. In RS-485 mode, the SD4008 listens on the 2-wire bus for receive data until it is required to send data. In RS-485 send mode it stops receiving, enables its transmitters when there is data to be sent, transmits the data and returns to receive mode. This eliminates the possibility of collisions with other devices which share the RS-485 bus and avoids receiving bogus stale echoed data. 
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