6.6.2. MODEM CIRCUIT OPERATION
The modem (IC505) has all the hardware satisfying the CCITT standards mentioned previously. When the ASIC IC501 (77) is brought to a low level, the modem (IC505) is chip-selected and the resistors inside IC are selected by the select signals from ASIC (IC501) ADR0-ADR4(pin 107~111). Commands are written through the data bus, and all processing is controlled by the ASIC (IC501) according to CCITT procedures. Here, the INT signal dispatched from IRQ (pin 52 of IC505) to the ASIC (IC501) implements post processing. This modem (IC505) has an automatic application equalizer. With training signal 1 or 2 at the time of G3 reception, it can automatically establish the optimum equalizer. The modem (IC505) clock is supplied by pin 70 of ASIC (IC501).
1. Facsimile Transmission/DTMF Line Send The digital image data on the data bus is modulated in the modem (IC505), and sent from pin 44 via amplifier IC511 (24 25), and the NCU section to the telephone line. Refer to 2.3.3.5. Analog Board Section. 2. Facsimile Reception The analog image data which is received from the telephone line passes through the NCU section and enters pin 45 of the modem (IC505). The signals that enter pin 45 of the modem (IC505) are demodulated in the board to digital image signals, then placed on the data bus. In this case, the image signals from the telephone line are transmitted serially. Hence, they are placed on the bus in 8 bit units. Here, the internal equalizer circuit reduces the image signals
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