During pulse dialing, this circuit opens to prevent pulse distortion caused by capacitor C11. When 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 the 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 (S5-1 to 5-2)

These circuits set the impedance according to the line requirement.

S5-1: 370 ohm + 620 ohm//310 nF (UK)

S5-2: 600 ohm (F)

H DC resistance switches (CN26 and CN36)

These switches set the DC resistance according to the line requirement.

Q FICC (IC6)

This circuits reduces the DC resistance to increase the loop current momentarily to assure operation of the switch at line seizuring.

R Constant current circuits (Q1 and Q2)

These circuits provide DC characteristics according to the French line requirement.

S Shunt (RL5)

This circuit prevents bell resonances in the telephone sets connected in parallel during pulse dialing and also reduces distortions of the pulse waveform.

T Communication line terminal switches (CN26 and CN36)

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