B&B Electronics 4WSD9TB - Datasheet - Manual (Page 4)

4WSD9TB-0712 - p4/5
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ICS
The 4WSD9TB does not require any handshaking lines to control the driver in RS-422 or RS-485 mode.
When Switch 1 set to RS-422, the driver is always enabled. When switch 1 is in the RS-485 position, the
RS-485 driver is automatically enabled during each Space state by the RS-232 data. During the Mark or
idle state, the RS-485 driver is disabled and the data lines are held in the Mark state by Bias provided by
the 4.7K Ohm pull-up and pull-down resistors. The value of these resistors may need to be changed to a
different value when termination is used in order to maintain the proper DC bias during the idle state. See
B&B El
ectronics’ free RS-422/RS-485 Application Note for more information on termination and DC biasing
of an RS-485 network.
RS-485 2-Wire Half Duplex
This communications mode is used to connect several RS-485 devices to the same network with a
minimum number of wires when only one unit talks at a time. All units are normally in Receive mode,
listening for data. When data is requested, the addressed device waits (1 delay time) then transmits,
afterwards, goes back to receive. To use this mode set Switch 1: RS-485 , Switch 2: Echo Off, and
Switches 3 and 4 to 2-Wire. Refer to Figure 1 for connections.
RS-485 4-Wire Full Duplex
This mode is used for 4-Wire Master/Slave. Devices can be polled and respond faster, unlike half duplex
mode, no turn-around time delay is needed between requests and responses. The RS-485 driver works the
same as in haft duplex but the receiver is always enabled. This can allow devices to receive information
even while they are responding to a request. To use RS-485 4-Wire mode, set Switch 1: RS-485, Switch 2:
Echo On, and Switches 3 and 4 to 4-Wire. When the 4WSD9TB is used as a Master in a single master
system, Switch 1 can be set RS-422 since it is the only transmitter. When used for a Slave device, the RS-
232 device must provide addressability, and RS-485 mode should be selected. As in 2-Wire operation RS-
485 Biasing is provided on Receive, and should be provided on the transmit pair by the End-of-Line slave
device, RS-422 Transmit mode requires no bias on transmit. Refer to Figure 2 for Connections.
RS-422 4-Wire Full-Duplex or 2-Wire Simplex
This communications mode is typically used for point-to-point communications over long distances with
better noise immunity than RS-232. Another common use is as a single master in a master/slave
configuration, where the slave devices only receive, but don’t transmit back. In RS-422 the transmitter and
receiver are always enabled to allow full-duplex communications. Connections require one twisted pair for
Transmit, another twisted pair for Receive and a ground reference wire
i
for a total of 5 lines to operate
properly. To set this mode, Table 1: Switch 1: RS-422, Switch 2: Echo On, and Switches 3 and 4: 4-wire
Specifications
Signals:
o Transmit (TD) and Receive (RD)
o RTS and CTS are looped back, DTR., DSR & CD are looped back
Data Rates:
o Up to 115.2 kbps
Distance:
o Externally powered transmits up to 4000 ft (1200 m) at 115.2 kbps (may be less with port
powering)
Dimensions:
o 3.6 x 1.7 x 0.9 in (9.0 x 4.3 x 2.3 cm)
Temperature:
o 0-70 C
Troubleshooting Operation
If a RS-485 or RS- 422 device doesn’t respond to data requests, try swapping the polarity of the data lines.
Some devices are marked opposite the RS-485 or RS-422 Standard. 4-Wire devices must swap polarity of
each pair. Operation of the converter can be checked with HyperTerminal. Set Converter to Loopback Test
mode. Open HyperTerminal using the Com port connected to, set baud rate, set Flow Control to None,
type characters. Each character should show as typed, two if local echo is on. For more info, visit our
website, Technical Library, FAQ on Troubleshooting and Checking.
i If you are concerned about creating ground loops by connecting grounds of units together, please check into B&B Electronics’ line of
optically isolated RS-232 to RS-422/485 units such as the 485OT9L.
This product is Designed and Manufactured in the USA of domestic and imported components.