54
W&T
USB Interfaces
Wiring configuration
The 20mA termination of the Interface is implemented as a DB9
plug. The pin assignments for the connector can be found in
the following table as well as on a sticker applied to the unit.
Display elements
The interface has two green LEDs. The On Line LED indicates
that the interface has a connection to the driver software and
that the software has activated the serial interface circuitry. The
Data LED indicates data activity in both directions.
Modes
The Interface can be used both as an active and a passive 20mA
component. In active mode the Interface provides the loop
current for the respective 20mA loop, whereas in passive mode
the connected device must provide the loop current.
The mode can be selected separately over the external
configuration of the Interface. Examples for configuring the
Interface in active and passive mode can be found in the
following application examples.
A GND level signal on Pin 5 of the SUB-D connector will place
the module in half-duplex mode whereby an echo of the sent
signals is suppressed.
pin#
signal
1
Data Out 20mA
2
Data Out +
3
Data Out -
4
Data Out GND
5
Half Duplex Control
6
Data In 20mA
7
Data In +
8
Data In -
9
Data In GND
