USB
to Serial Adapter
24
Operating Mode (MEI adapters only)
RS-232 (default)
This mode configures the serial port to use an RS-232 electrical
interface. Each UART's transmit drivers and receivers are always
active in this mode.
RS-422/485 Full Duplex (4-wire)
This mode configures the serial port to use an RS-422/485 electrical
interface. Each UART's transmit drivers are always active in this
mode. This mode allows simultaneous transmit and receive
operation. Transmit and receive data move over separate dedicated
pairs of conductors in the attached cable. The AuxOut/AuxIn signals
are also available in 4-wire mode.
RS-422/485 Half Duplex (2-wire) Auto-Toggle
This mode configures the serial port to use an RS-422/485 electrical
interface. Transmit and receive operations share a single pair of
conductors in the attached cable, so communication occurs in only one
direction at a time. 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.
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.
Note: The serial port’s LED
will glow red in RS-232 mode.
Note: The serial port’s LED
will glow green in RS-422/485
mode.
Note: The serial port’s LED
will glow green in RS-422/485
mode.
