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8.13. BELL SIGNAL GENERATOR
Bell signal for ringing an SLT is generated by amplifying the 20 or 25Hz square wave provided
from MPR card to AC75Vrms onboard. The SW power supply in the BELL circuit generates
between +160V and 100V of voltage by switching the +40V form the power source at 125KHz
frequencies. Bell signal picks up the square wave provided from MPR via a photocoupler, and it
transforms into SIN wave, then amplified to AC75Vrm bell signal by the amplitude between +
160V and -100V of voltage (Mainly +30Vdc) produced by SW power supply. When the Bell signal
is not needed, bell signal voltage generating circuit can be turned off by transmitting H signal
from P21 port (BELL CNT) of ASIC to reduce the power consumption.
8.14. BELL SIGNAL TRANSMISSION
A 75V bell signal generated onboard is transmitted to the individual port, then control the bell
ON/OFF by making a bell relay in each port (Bell signal ON) and by breaking it (Bell signal OFF).
The 16 ports do not ring simultaneously. They are divided into 4 layers to control ON/OFF. They
are divided in to following 4 groups (The ports in the same group ring simultaneously.): "1, 5, 9,
13", "2, 6, 10, 14", "3, 7, 11, 15" and "4, 8, 12, 16".
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