144

Audio ICs

BU2618FV

S Frequency counter

(1)

Structure

(2)

How the frequency counter operates

When control data CT equals 1, the 20-bit counter

and the amp go into operation. When CT equals 0,

amp input goes to pulldown and the counter is re-

set. Measuring time (gate pulse) is selected

(16ms / 32ms) on the basis of control data GT.

When control data CT equals 0, the counter is reset.

(3)

Explanation of output data

Unlock detection

When control data GT equals 1, or CT equals 1, the

unlock detection circuit goes into operation for 8 ms.

When CT equals 1, the unlock detection circuits

stops operating before the frequency counter gate

pulse is emitted. When CT equals 0, or GT equals

0, the unlock detection circuit is reset.