7.11.2. CIRCUIT OPERATION
The TAM INTERFACE circuit consists of an EXT. TAM HOOK detection circuit, CNG signal from
the other party’s detection circuit, VOX detection circuit (to judge sound/no-sound) and RLY101
(to separate EXT. TAM).
1. EXT. TAM HOOK detection circuit
A bell is received at EXT. TAM and EXT. TAM is connected to the
line, making a DC LOOP. Then, PC105 detects this voltage. During
detection, PC105 (4) becomes low.
(DC LOOP)
Tip L102 PC105 (2, 1) L105 Tip1 (EXT.TAM) Ring 1
L104 RLY101(5, 3) L103 POS101 Ring
2. CNG/VOX signal detection circuit
The CNG signal from the other party’s FAX is detected in MODEM
IC505 (digital board).
(Signal path)
Refer to CHECK SHEET().
3. Remote receiving
This is the parallel-connected DTMF signal for the TEL or EXT.TEL
mode between T and R. When the other party is a FAX, the unit
switches to FAX receiving.
(Signal Path)
Detects the DTMF signal in the MODEM.
7.12. OPERATION BOARD SECTION
The unit consists of a LCD (Liquid crystal display) and KEYs. They are controlled by the Gate
Array (IC301) and ASIC (IC501: on the DIGITAL BOARD).
The key matrix table is shown below.
Key Matrix
187
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