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Circuit PWI - Power Indication (CCITT 213)
Direction: FROM 7500
The ON condition indicates that power is on at the 7500.
Circuit DLO - Data Line Occupied (CCITT 203)
Direction: FROM 7500
The ON condition of this circuit indicates that the communication channel is in use.
The OFF condition indicates that the DTE may originate a call provided that its PWI is ON.
Circuit DSC - Distant Station Connected (CCITT 204)
Direction: FROM 7500
Signals on this circuit indicate whether a connection has been established to a remote data station.
This circuit turns ON in response to receipt of a Call Connected packet for X.25 virtual call set-up
and in response to a Connect message for B channel circuit switched data call set-up. Control of the
communication channel is transferred to the associated EIA-232D interface. When Circuit DSC is
turned ON, the DTE may turn Circuit CRQ OFF without causing a communication channel disconnect.
Disconnection of the channel by the DTE is then possible only through the associated EIA-232D
interface.
Once Circuit DSC is turned ON, it remains On until Circuit CRQ is turned OFF by the DTE. After
Circuit CRQ is turned OFF by the DTE, Circuit DSC is turned OFF.
Circuit ACR - Abandon Call and Retry (CCITT 205)
Direction: FROM 7500
the ON condition indicates that the call should be abandoned, and remains ON until the DTE turns off
circuit CRQ. Circuit ACR turns ON upon receipt of any packet or message from the network other than
a Call Connected packet or Connect message. Circuit ACR also turns On if Circuit CRQ is ON when
the 7500 enters any test mode.
The OFF condition indicates the call origination can proceed.
Circuit ACR remains in the OFF condition after Circuit DSC is turned ON.
Digit Signal Circuits
Direction: TO 7500
Circuit NB1 - Low Order Binary (2) (CCITT206)
Circuit NB2 - Second Order Binary (2) (CCITT207)
Circuit NB4 - Third Order Binary (2) (CCITT208)
CHAPTER 9: TECHNICAL INFORMATION
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