Brother LX-200, Service Manual

Page: 115 / 177

5-7
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Buzzer Drive Circuit
This circuit sounds the piezoelectric buzzer.
To sound the buzzer, the main CPU outputs a 4 kHz squarewave with 50% duty
from port DV0 (P13). This signal is used to generate the buzzer sound.
To stop the buzzer, the port status is set to High level using R82 in the input mode.
Fig. 5.3-4 Buzzer Drive Circuit
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LED Drive Circuit
This circuit drives the red and green LED indicators mounted on the switch LED and
lights the Power button red, green, or orange.
The LED s are directly driven by the high-current ports P32, P33, P34, and P35 of
the main CPU. The LED lights when the corresponding output is Low.
When not lit, the LED is in the high-impedance status and the port level is
indeterminate.
Fig. 5.3-5 LED Drive Circuit