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SHM-B ASYNC
Because DTR, DSR, RTS, and CTS are tied together
internally, dropping any one of these four signals to a
negative state will also drop DCD on the remote side to a
negative state. DCD will also go LOW if the remote
SHM-B is powered down, or if the twisted-pair wire is
broken.
X-ON/X-OFF M
ODE
(RTS/DTR C
ONTROL
J
UMPER IN
DIS P
OSITION
)
If X-ON/X-OFF characters are used for handshaking
control, rather than hardware logic levels, move the
RTS/DTR control jumper to the DIS position.
Typically, units that use software X-ON/X-OFF flow
control do not want RTS to affect DCD on the remote
SHM-B. Moving the jumper to the DIS position disables
the RTS/DCD relationship. The only thing that will
force DCD low with the jumper in the DIS position is the
absence of power on the remote SHM-B or a broken
twisted-pair wire.