Formatter in the fax subsystem The formatter contains the modem chipset (DSP and CODEC) that controls the basic fax functions of tone generation and detection, along with channel control for the fax transmissions. The CODEC and its associated circuitry act to control transmit and receive gains, and compensate for transmission signal coupling into the receive channel. Also on the formatter is circuitry to add termination impedance to help match the telephone network impedance. LIU in the fax subsystem Two versions of LIU are used in the HP LaserJet 3330mfp. One is used in the Americas and for Asia. The other is used primarily in Europe. Differences in the European version include:
a different voltage protection device current limiting of the DC current filtering for the countries that use billing or metering tones control of the impedance of the DC circuit via SHUNT signal Due to the lack of polarization on TIP and RING, all LIU circuitry that connects to TIP and RING is bi-directional. The LIU operates identically when TIP and RING are reversed. The rest of this section describes the hardware functions of the LIU.
Safety isolation The most important function of the LIU safety isolation between the high-voltage, transient prone environment of the telephone network (TNV - telephone network voltage) and the low-voltage analog and digital circuitry of the formatter (SELV - secondary extra low voltage). This safety isolation provides both customer safety and product reliability in the telecom environment. Any signals that cross the isolation barrier do so either optically or magnetically. The breakdown voltage rating of barrier-critical components is greater than 1.5kV. EN LIU (fax) functions and operation 101