16.5. Locator Mode1. When the base unit LOCATOR button is pressed, the IN USE (LED903) is flashed.16.6. Telephone Line InterfaceTelephone Line Interface Circuit:Function•••• Bell signal detection•••• ON/OFF hook and pulse dial circuit•••• Side tone circuit•••• Auto-disconnect circuit/Parallel connection detection circuitBell signal detection and OFF HOOK circuit:In the idle mode, Q4 is open to cut the DC loop current and decrease the ring load. When ring voltage appears at the Tip (T)and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:T, R → L1, L2 → R30, R31 → C16, C17 → Q6 → DSP (BELL) [BELL]When the CPU (DSP) detects a ring signal, Q4 turns on, thus providing an off-hook condition (active DC current flow throughthe circuit) and the following signal flow is for the DC line current.T → D4 → Q4 → Q1 → R5 → D1 → D4 → L2 → POS1 → R [OFF HOOK]ON HOOK Circuit:Q4 is open, Q4 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-hookcondition.Pulse Dial Circuit:DSP (RYL) turns Q4 ON/OFF to make the pulse dialing.Side Tone Circuit:Basically this circuit prevents the TX signal from feeding back to RX signal.As for this unit, TX signal feed back from Q1 is canceled by the echo canceller of DSP.Note: DSP is IC201.See CPU DATA (BASE UNIT) (P.59)50KX-TG2220BXB / KX-TG2220BXF / KX-TG2220BXS / KX-TGA226BXB / KX-TGA226BXF / KX-TGA226BXS
