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18 — RS-232 DCM
2902 MainStreet Technical Practices 18-5
May 2002 90-2906-01
18.7 Control signals
Control signals provide the handshaking required for call setup, call tear-down and
synchronization. Control signals can be configured as:
•
high (ON)
•
low (OFF)
•
end-to-end (END_TO_END)
End-to-end means the state of the local signal follows that of the signal source at the
remote end of the network. This option is only available for HCM rate adaption.
The supported control signals for the RS-232 DCM depend upon the operating mode
of the circuit. Table 18-1 shows the default states of the supported control leads for
the various operating modes.
Table 18-1 RS-232 DCM control signals
Note
(1)
RTS-CTS signaling is supported locally when CTS is configured END-TO-END. RTS-DCD
end-to-end signaling is not supported. DTR and DSR are not functional. An RTS lead raised on the
local end is propagated to the remote end as DCD. The remote end must be able to extract the lead
as DCD and pass it on to the user equipment. RS-232 DCMs have limited control lead capability;
therefore, they cannot extract and pass on the DCD lead to be output as CTS. In order to operate in
sync DCE mode, then, the user must have an EIA/TIA-232 DTU at the remote end providing full
control lead support.
Operating mode Inputs Outputs
Async DCE RTS
DTR
END_TO_END
END_TO_END
CTS
DSR
END_TO_END
FORCED ON
Async DTE DCD
DSR
END_TO_END
END_TO_END
RTS
DTR
END_TO_END
FORCED ON
Sync DCE (Slave or External)
(1)
RTS END_TO_END CTS END_TO_END
Sync DTE (Internal) — — RTS END_TO_END
Sync DTE (Slave or External) DCD END_TO_END RTS END_TO_END