Communication Modes
The cards support Simplex, Half-Duplex, and Full-Duplex communications in a variety of 2- and
4-wire cable connections. Simplex is the simplest form of communications with transmission
occurring only in one direction. Half-Duplex allows traffic to travel in both directions, but only one
way at a time. In Full-Duplex operation, data travels in both directions at the same time. Most
RS485 communications use the half-duplex mode because only a single pair of wires need to be
used and installation costs are dramatically reduced. The cards also support the option of locally
echoing the characters back to the transmitter.
RTS and Auto Transceiver Control
In RS485 communications the driver must be enabled and disabled as needed, allowing all cards
to share a two wire or four wire cable. These cards have two methods of controlling the driver;
automatic (Auto) and request-to-send (RTS) control. With automatic control, the driver is enabled
when data is transmitted. The driver remains enabled for the transmission time of one character
and then is disabled. The cards automatically adjust their timing to the baud rate of the data.
(Note: For use with Windows programs in half-duplex mode, card must be operated in the Auto
mode.)
Under RTS control, your software must set the RTS bit to a logic "1" to enable the driver and logic
"0" to disable the driver.
The receiver is also normally disabled during RS485 transmissions. See the Option Selection
section for details on setting the Auto and RTS modes, and for enabling or disabling local echoing
of characters. In normal RS485 communication the echo is turned off to prevent data being
echoed back.
CE Mark
If your card is CE-marked, it meets the requirements of EN50081-1:1992 (Emissions), EN50082-
1:1992 (Immunity), and EN60950:1992 (Safety).
Manual PCI-COM-2S
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