7.4. TONE GENERATION CIRCUIT
Function:
This circuit generates all system tones including COL, extension, busy, DTMF signals and key in
confirmation tones during the power failure mode and is comprised of IC1(DTMF Generator) and
IC5 (Analog Switch).
Circuit Operation:
For an output of a single row tone, the row terminal and the each column terminals intersecting
with it are required to be brought a low state. For a dual tone output, one row terminal and one
column terminal are brought to low state.
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