DP120F/DP125F Circuit Description 7-88 March 2000 © TOSHIBA TECThe line monitor circuit consists of the CML relay (US/CA/TW: RLY2, EU/AU/ASIA/HK: RLY3),analog switch (US/CA/TW: IC51, EU/AU/ASIA/HK: IC3), the I/OP-1 GA (IC7) and analog switches(IC8, IC14) on the Main PBA, and other peripheral devices. It switches the telephone line pathwith the analog switch and monitors the line status, ringer signal, and tone signal in facsimiletransmission and reception with the speaker connected to CN5 on the Main PBA. It also switchesthe analog switch to output a buzzer tone from the speaker.The signal to be monitored is selected by switching the analog switch (IC8) according to theMONISEL signal, TONESEL signal, and RING/TONE signal which are output from the I/OP-1GA.To monitor the line during transmission and reception, the I/OP-1 GA causes the CML1 signalto be HIGH to switch the analog switch and connect the line to the MODEM side.For line path switching control, refer to "4. 1 Line Path Switching Control Circuit" in this chapter.The correspondence between the respective signal levels and monitoring signals is shown inthe table below.The monitoring signal selected by IC8 is input to the analog switch (IC14) to select an outputsound volume. The sound volume is selected by switching IC14 according to the SPVOL0-2signals output from the I/OP-1 GA and selecting an input resistance for the monitoring signal.The correspondence between the respective signals and sound volumes is shown in the tablebelow.Monitoring signal MONISEL TONESEL RING/TONELINE Monitor Line 1 HIGH HIGH -Line 2 LOW HIGH -Ringer - LOW HIGHAlarm/Key touch Tone - LOW LOWSound volume SPVOL2 SPVOL1 SPVOL0Silent (0) LOW LOW LOWMin. (1) LOW LOW HIGH(2) LOW HIGH LOW(3) LOW HIGH HIGH(4) HIGH LOW LOW(5) HIGH LOW HIGH(6) HIGH HIGH LOWMax. (7) HIGH HIGH HIGH
