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CHAPTER 4: DEFINITIONS OF 7500 OPTIONS
DCD (Data Carrier Detect)
Configurations: Asynchronous DCE, Asynchronous DTE
Data Protocols: X.25, Mode 2, Mode 3
Asynchronous DCE
This option determines whether the 7500 turns on the Data Carrier Detect (DCD) lead when a data
call is in progress, and off when one is not (follow), or whether it keeps DCD on essentially all the
time (ignore).
If your data terminal transmits data only when the Data Carrier Detect lead is on, set DCD to
ignore. When the DCD lead is set to ignore, it appears to your terminal that a data call is always
present, except for one second following termination of a call. This will enable your data terminal to
transmit commands to the 7500 even when a data call is not present. This setting is appropriate for
most users.
Set the DCD lead to follow only if your data terminal requires that Data Carrier Detect be off when
a data call is not present. Select follow also if your terminal will not enter data mode unless it sees the
Data Carrier Detect go from off to on.
See the instruction manual for your data terminal to determine which setting is appropriate.
Asynchronous DTE
This determines how the 7500-DTE responds to changes in the state of the attached modem's DCD
lead.
Many modems use the DCD lead to indicate the presence or absence of carrier. During power
interruptions, carrier may be momentarily absent without disconnecting the data call. These modems
use Data Set Ready (DSR) to indicate that a call has been disconnected. Other modems drop DCD only
when a call has been disconnected. In addition, such modems may keep DSR on whether a call is
present or not. The DCD option allows you to select the method of automatically ending data calls that
is appropriate to your attached modem.
If your modem uses DCD to indicate presence or absence of carrier, regardless of the state of the
call, you should set this option to ignore. This will prevent undesired disconnections when momentary
interruptions in carrier occur.
If your modem drops DCD only when a call is disconnected and does not drop DSR, set DCD to
follow. The 7500-DTE always disconnects the call if DSR is dropped.
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Synchronous DCE
Option Values For Data.rest
Front Panel
Without Help
With Help
0
OFF
1
ON
CMD
Factory Value
Mode
DCE
X
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