Panasonic KX-FM330GR Service Manual page 215

6.9.4. BELL DETECTION CIRCUIT
1. Circuit Operation
The signal wave form of each section is indicated below. Signal (low level section) input to pin 29 of gate array IC5 is read out
at the CPU and judged as a bell.
TEL LINE → PC2 (1,2) → PC2 (4) → IC5(29)
6.9.5. PULSE DIAL CIRCUIT
1. Circuit Operation
In the OFF-HOOK condition, the photocoupler PC3 pin (2) is a low level by the IC5 pin (2), and the PC3 pin (4) is a low level
if Q3 is ON. During the pulse dial operation, the PC3 pin (2) becomes a high level by the IC5 pin (2), so that the PC3 pin (4)
becomes a high level. If Q3 is ON, then the line is ON and vice versa. The high/low control for the IC5 pin (2) makes the pulse
dial operation possible.
· IC5 (2) High Level → PC3 (2) High Level → PC3(4) High Level → Q3 OFF → TEL LINE OFF
· IC5 (2) Low Level → PC3 (2) Low Level → PC3(4) Low Level → Q3 ON → TEL LINE ON
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KX-FP320G / KX-FM330G