KX-NCP1173XJ (serv.man2) - Panasonic PBX Service Manual (repair manual). Page 8

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• CODEC control......IC300

Infineon-manufactured PEB2466 is used. The analog characteristics, such as BN, frequency characteristic, level, and sidetone,
are set by the CODEC interface DCLK, CS, DOUT, and DIN. The built-in I/O port is used for HOOK detection, DTMF detection,
BELL relay control, and DIAG relay control.

• A/D, D/A conversion

The conversion of 4-line analog signal and G.711 format PCM code (

µ/A) is carried out.

• SLT current-supply circuit

The current-supply circuit feeds current at the constant-current circuit. When the telephone is taken off the hook, DC loop is
formed.
The feeding current is limited to 30mA by the circuit configurations of R59, Q53, R60, and Q54.
+40VTR 

→ R62 → R59 → Q52 → RL52(b → c) → L203 → L204 →R L52(c →b) → Q51 → R60 → R61 → SLTG(0 V)