B&B Electronics QSPXP-100 - Manual - Manual (Page 30)

Using configuration utilities B&B Electronics ExpressCard Serial Adapter User’s Manual
Page 26 Rev 1.00 (July 2007)
RS-422/485 Full Duplex (4-wire)
This mode allows simultaneous transmit and receive operation.
Transmit and receive data move over separate dedicated pairs of
conductors in the attached cable. Each UART's transmit drivers are
always active in this mode. The AuxOut/AuxIn signals are also
available in 4-wire mode.
RS-422/485 Half Duplex (2-wire) Auto-Toggle
This mode only permits data to flow in one direction at a time.
Transmit and receive operations share a single pair of conductors in
the attached cable. This configuration is often referred to as
“multidrop.”
The transmit drivers are automatically enabled before data is
transmitted, then disabled immediately after all data has been
transmitted. This feature is implemented in hardware for near-
instantaneous response.
RS-422/485 Half Duplex (2-wire) RTS control
The half-duplex operation is the same as in the Auto-Toggle mode,
except that the RTS signal is used to control the transmit drivers
instead of the automatic control.
The software application can disable the port's transmit drivers by
deasserting the UART's RTS output. To allow transmission again, the
software application must assert the RTS output.
RS-422/485 Half Duplex (2-wire) DTR control
This mode operates the same as Half Duplex using RTS, except that
the UART's DTR output is used.
Note: The Auto-Toggle mode is
the best choice for most half-
duplex scenarios. It offers the
best performance and the best
ease-of-use.