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Pin 20 - Data Terminal Ready (CD)
This lead allows the attached data terminal to control the 7500's connection to the network. When
the DTR option is set to follow, the 7500 requires an ON condition of Pin 20 to interact with the
attached terminal or to initiate or maintain a data connection or test sequence (except the local self-test).
If the attached data terminal turns off the DTR lead for more than 50 milliseconds during data call
setup, while in the data transfer mode or during a test sequence, the 7500 clears the call or terminates
the test.
When the DTR option is set to ignore, the 7500 will act as if the DTR lead is always ON.
Additionally, if the DTR option is set to ignore and the answer option is set to AUTO, the 7500 will
automatically answer an incoming data call even if there is no data terminal equipment attached. This is
useful for remote loopback testing of new installations.
Pin 21 - Remote Loopback (RL)
When the attached data terminal turns this lead ON, the 7500 enters remote loopback test mode.
When the attached data terminal turns this lead OFF, the 7500 ends the remote loopback test.
Pin 22 - Ring Indicator (CE)
The 7500 transmits a pulsed signal on this lead when it receives an incoming call. Generally, the
7500 maintains this pulsed signal until either the call is answered or disconnected. The lead remains
ON for a minimum of one second even if the call is answered before that second. The cadence of the
pulse simulates ringing: two seconds ON, four seconds OFF. The 7500 maintains an OFF condition on
this lead at all other times.
Pin 25 - Test Mode (TM)
The 7500 turns this lead ON when
the attached data terminal turns on the Remote Loopback or Local Loopback leads
a Local or Remote Loopback test is enabled through the commands typed on the keyboard of an
attached data terminal
a Local or a Remote Loopback test is enabled from the front panel of the 7500
a Remote Loopback is initiated by the far-end.
The 7500 turns this lead OFF when the test condition is ended.
CHAPTER 9: TECHNICAL INFORMATION
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