B&B Electronics 3PCIU4 - Manual (Page 15)

Serial Card Setup
Manual Documentation Number 3PCIoUx-1008 Chapter 2 9
Overview of Operational Modes
RS-232 Mode
In RS-232 Mode MIport serial ports function as buffered standard PC serial
ports and operate as DTEs (Data Terminal Equipment). RS-232 interfaces are
commonly used for communications with modems, serial printers, and
computer-controlled devices such as security equipment, bar code scanners
and point-of-sale devices.
For most MIport models, RS-232 Mode supports eight single-ended signal
lines and signal ground (GND) including transmit (TD), receive (RD) and six
hardware handshake lines (DTR, DSR, RTS, CTS, DCD, RI). The only
exception to this is the MIport Model 3PCIOU4 card, which supports TD,
RD, RTS, CTS and GND.
RS-422 Mode
In RS-422 mode MIport serial ports provide two sets of differential signal
pairs (TD and RD) and signal ground for each port. The RS-422 standard
uses balanced differential drivers and receivers for each signal. This
facilitates greater communication distances than unbalanced systems such as
RS-232. In RS-422 mode the transmitter and receiver are always enabled (TX
ON, RX ON).
RS-422 operation is suitable for interconnecting a computer and one device
for full duplex (point-to-point) bi-directional communication, or a computer
and several devices for unidirectional (point-to-multipoints) communication.
RS-422 interfaces are commonly used for video editing/control, camera
control, electronic signage, television studio/satellite dish control,
performance lighting and audio equipment control.
RS-485 Mode
In RS-485 Mode MIport cards provide RS-485 interfaces which operate with
the same signals and signal levels as RS-422. RS-485 interfaces differ from
RS-422 in that they allow multiple devices to share the same communication
link using half duplex (2-wire) or full duplex (4-wire) connections. Since it is
possible to have more than one transmitter connected to the media,
transmitters must be enabled only while sending data, and tri-stated at all
other times so other devices can use the wire pair. MIport cards automatically
enable the transmitter at the appropriate time using Automatic Send Data
Control, based on the contents of the output buffer. When the buffer has data
to send, the transmitter is enabled (TX SD). When all data in the buffer has
been sent, the transmitter is disabled and tri-stated to a high impedance state.