ADLINK Technology cPCI-3938, Manual

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Expansion/Isolation Module User Guide
Because RS-422 interface do not use DTR/DSR/DCD signal, user may not
use DTR/DSR handshake and DCD signal checking function in its
application, these signals are in inactive condition for RS-422 interface.
RS-485 interface application note:
RS-485 interface is used for multi -drop half-duplex application. Because
we had put auto -direction capability in the box, user may not use RTS
signal to control the data direction. So it is no use for RTS/CTS signal in
RS-485 interface. Because we had put one 120 ohm terminator resistor in
RXD input signal pair, user may need to remove this terminator resistor for
proper operation.
Due to proper operation, user may not let one cable left in unconnected
condition. Because the crosstalk problem may let one transmit data signal
to be coupled to receive data input. This may lead wrong process in some
application environment.
Because RS-485 interface do not use RTS/CTS/DTR/DSR/DCD signal,
user may not use RTS/CTS or DTR/DSR handshake and DCD signal
checking function in its application, these signals are in inactive condition
for RS-422 interface.