HP laserjet 3390, 3392 all-in-one Manuale Di Servizio
Data path
The magnetically coupled signals that cross the isolation barrier go either through a transformer or a
relay. The TIP and RING signals use a transformer to cross the isolation barrier.
relay. The TIP and RING signals use a transformer to cross the isolation barrier.
TIP and RING are the two-wire paths for all signals from the telephone network. All signaling and data
information comes across them, including fax tones and fax data.
information comes across them, including fax tones and fax data.
The telephone network uses dc current to determine the hook state of the telephone, so line current
must be present during a call. On some line interfaces this current flows through the transformer, but
on the LIU, a capacitor blocks the current from going into the transformer.
must be present during a call. On some line interfaces this current flows through the transformer, but
on the LIU, a capacitor blocks the current from going into the transformer.
Blocking the current with a capacitor prevents the core of the transformer from being saturated by the
high dc voltage, which can affect the ac signal quality. Rather than permitting the current to flow through
the transformer, this LIU directs the current through another circuit called a gyrator or dc hold circuit.
This creates the path for the central office-current flow when a call is in progress.
high dc voltage, which can affect the ac signal quality. Rather than permitting the current to flow through
the transformer, this LIU directs the current through another circuit called a gyrator or dc hold circuit.
This creates the path for the central office-current flow when a call is in progress.
Hook state
Another magnetically coupled signal is the control signal that disconnects the downstream telephone
devices (such as a phone or answering machine). A control signal originating on the formatter can
change the relay state, causing the auxiliary jack (downstream jack) to be disconnected from the circuit.
devices (such as a phone or answering machine). A control signal originating on the formatter can
change the relay state, causing the auxiliary jack (downstream jack) to be disconnected from the circuit.
The all-in-one takes control of calls that it recognizes as fax calls. If the all-in-one does not directly pick
up the call, it monitors incoming calls for the fax tone or for the user to direct it to receive a fax. This idle
mode is also called eavesdropping. This mode is active when the all-in-one is on-hook but current exists
in the downstream phone line because another device is off-hook. During eavesdropping, the receive
circuit is enabled but has a different gain from the current that is generated during normal fax
transmissions.
up the call, it monitors incoming calls for the fax tone or for the user to direct it to receive a fax. This idle
mode is also called eavesdropping. This mode is active when the all-in-one is on-hook but current exists
in the downstream phone line because another device is off-hook. During eavesdropping, the receive
circuit is enabled but has a different gain from the current that is generated during normal fax
transmissions.
The all-in-one does not take control of the line unless it detects a fax tone or the operator tells it to
connect manually. This feature allows the user to make voice calls from a phone that is connected to
the all-in-one without being cut off if a fax is received.
connect manually. This feature allows the user to make voice calls from a phone that is connected to
the all-in-one without being cut off if a fax is received.
Downstream current detection
The aux phone detect signal is optically coupled. This signal tells the firmware that an active phone (or
modem or answering machine) is connected to the auxiliary port of the all-in-one (the right side of the
RJ-11 jack).
modem or answering machine) is connected to the auxiliary port of the all-in-one (the right side of the
RJ-11 jack).
A circuit that can detect current above a certain threshold generates the downstream-current-detection
signal. The downstream current goes through a resistor, generating a voltage. If this voltage is above
the threshold level, the signal changes state.
signal. The downstream current goes through a resistor, generating a voltage. If this voltage is above
the threshold level, the signal changes state.
The downstream-current-detection signal is coupled back to the formatter through an optoisolator and
across the safety isolation barrier. The firmware uses this signal to ensure that the all-in-one does not
go off-hook (and disconnect a downstream call) until it has been authorized to do so (by a manual fax
start or detection of the appropriate tones).
across the safety isolation barrier. The firmware uses this signal to ensure that the all-in-one does not
go off-hook (and disconnect a downstream call) until it has been authorized to do so (by a manual fax
start or detection of the appropriate tones).
ENWW
Fax functions and operation
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