Panasonic KX-T7456 - Digital 24 Button Speakerphone Display, Specifications

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7.3. LED CIRCUIT
1) Circuit Operation
The LED executes dynamic lighting for the status indicators, and control is executed by the
output ports C0 to C5 (column) and R0 to R9 of IC1.
A fixed pulse (T=1.82 msec) is output continuously from the/SCK1 terminal of IC9. This pulse is
counted and the output of IC1 is shifted sequentially from C0 to C5.
R0 to R7 of IC1 also output pulses, and the lighting of the LED is controlled by the timing of the
output ports C0 to C5.
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