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Note The DCD LED is an indicator of whether the 2120 is configured
for DCE or DTE operation. When configured for DCE, the DCD
LED will glow constantly except for when a session is being ter-
minated. When configured for DTE, the DCD LED will only glow
when a connection is established with the serial interface.
5.2 FLOW CONTROL AND SESSION CONTROL
Flow Control
Flow control settings control the flow of data between the Model 2120
and the device connected to the serial interface. The Model 2120 can be
configured for DCE or DTE operation.
With hardware flow control selected, the RTS (Request To Send) and
CTS (Clear To Send) signals control the flow of data between the Model
2120 and the device connected to the serial interface. RTS originates
from the DTE and is an input to the DCE. CTS originates from the DCE
and is an input on the DTE. When the Model 2120 is configured for DCE
operations, the DTE will turn RTS ON to indicate the 2120 to send data
to the DTE and OFF to stop the 2120 from sending data before the DTE
receive buffers overflow. The 2120 (DCE) will turn CTS ON to allow the
DTE to transmit data and OFF to stop the DTE from sending data before
the 2120 receive buffers overflow. The opposite is true when the 2120 is
configured for DTE operations.
With xon/xoff (software) flow control selected, the flow of data between
the Model 2120 and the device connected to the serial interface is con-
Table 3: Model 2120 Top Panel LED definitions
LED Description
TXD Blinks green to show that data is being transferred through the unit.
RXD Blinks green to show that data is being received.
Note The TXD and RXD LED’s indicate activity on either pin 2 or pin 3 on the
DB-25 connector depending on DTE/DCE mode.
DTR Glows yellow to indicate that the Data Terminal Ready signal is being detected
by the Terminal Server.
RTS Glows yellow to indicate that the Request to Send signal is being detected by
the Terminal Server.
CTS Glows yellow to indicate that the Clear to Send signal is being detected by the
Terminal Server.
DCD Glows yellow to indicate that the Data Carrier Detect signal is being detected by
the Terminal Server.
Note When there is no connection to the DB-25 side of the unit, the CTS,
RTS, and DCD LED’s stay lit at all times.
PWR Glows green to indicate that power is applied to the unit.