If this circuits detects MF or CNG tones without seizuring a line, it disconnects NT (5) to increase the input impedance and also sets the receiving sensitivity.

B MUTE (RL3)

During pulse dialing, this circuit opens to prevent pulse distortion caused by capacitor C11. If it detects MF or CNG tones without seizuring a line, it opens to

increase the impedance.

C Pickup RC (R590, C31)

These circuits insert a high-impedance resistor and capacitor serially to prevent the line impedance from dropping by the line transformer T1.

D Ring detectors (IC1)

These circuits detect a ring signal arriving to the line. If the input ring signal exceeds a specific voltage, the circuits output a signal of RI having the same

frequency as incoming RI.

E Line transformer (T1)

This circuit processes send/receive signals required for facsimile transmission, dial tone receive signals required for automatic dialing, and MF tone send and

remote receive signals. It separates between the line and equipment in terms of DC and also keeps a balance between the line and the ground.

F Off-hook detectors (IC2, RL7)

These circuits detect the off-hook state of the telephone connected to the TEL1, TEL2, through LINE terminals. IC2 uses a high detection sensitivity than of RL7.

In TEL/FAX mode, the higher sensitive IC2 is used to detect the off-hook state of the telephone while the main equipment is hunting a line. Usually, IC2 is

short-circuited by the CML relay (7) in the standby state and RL7 is used for off-hook detection.

G Impedance switches (S4-3 to S4-4)

These circuits set the impedance according to the line requirement.

S4-3: 220 ohm + 820 ohm//115 nF

S4-4: 600 ohm

I Ring impedance switches (S1-4)

These switches set the ring impedance according to the line requirement.

J Ring sensitivity switch (S4-4, S4-2)

This switch sets the ring sensitivity according to the line requirement.

K Telephone cascade/parallel switches (S1-1 to S1-2)

To connect the telephone connected to the TEL1 terminal and an external telephone in parallel, set the switches to ON.

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