Cooper Bussmann BU-945U-E 802.11 DSSS user manual DB9 Connector Pinouts, RS485 Serial Port

Cooper Bussmann Wireless Ethernet & Device Server BU-945U-E 802.11 DSSS User Manual

DB9 Connector Pinouts

Pin	Name	Direction	Function
1	DCD	Out	Data carrier detect
2	RD	Out	Transmit Data – Serial Data Output (from DCE to DTE)
3	TD	In	Receive Data – Serial Data Input (from DTE to DCE)
4	DTR	In	Data Terminal Ready
5	SG	- -	Signal Ground
6	DSR	Out	Data Set Ready - always high when unit is powered on.
7	RTS	In	Request to Send
8	CTS	Out	Clear to send
9	RI	- -	Ring indicator

RS485 Serial Port

The RS485 port provides for communication between the BU-945U-E unit and its host device using a multi-drop cable. Up to 32 devices may be connected in each multi-drop network.

As the RS485 communication medium is shared, only one of the units on the RS485 cable may send data at any one time. Thus, communication protocols based on the RS-485 standard require some type of arbitration.

RS485 is a balanced, differential standard but it is recommended that shielded, twisted pair cable be used to interconnect modules to reduce potential RFI. It is important to maintain the polarity of the two RS485 wires. An RS485 network should be wired as indicated in the diagram below and terminated at each end of the network with a 120-ohm resistor. On-board 120-ohm resistors are provided and may be engaged by operating the single DIP switch in the end plate next to the RS485 terminals. The DIP switch should be in the “1” or “on” position to connect the resistor. If the module is not at one end of the RS485 cable, the switch should be off.

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